Magnetic tape, magnetic tape cartridge, and magnetic tape apparatus

ABSTRACT

The magnetic tape includes a non-magnetic support; and a magnetic layer, in which the magnetic layer has a timing-based servo pattern, an edge shape of the timing-based servo pattern, specified by magnetic force microscopy is a shape in which a difference L99.9−L0.1 between a value L99.9 of a cumulative distribution function of 99.9% and a value L0.1 of a cumulative distribution function of 0.1% in a position deviation width from an ideal shape of the magnetic tape in a longitudinal direction is 180 nm or less, and an absolute value ΔN of a difference between a refractive index Nxy of the magnetic layer, measured in an in-plane direction and a refractive index Nz of the magnetic layer, measured in a thickness direction is 0.25 or more and 0.40 or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C 119 to Japanese PatentApplication No. 2019-016520 filed on Jan. 31, 2019. The aboveapplication is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape, a magnetic tapecartridge, and a magnetic tape apparatus.

2. Description of the Related Art

A magnetic recording and reproducing apparatus which performs recordingof data on a magnetic recording medium and/or reading (reproducing) ofthe recorded data is widely divided into a magnetic disk apparatus and amagnetic tape apparatus. A representative example of the magnetic diskapparatus is a hard disk drive (HDD). In the magnetic disk apparatus, amagnetic disk is used as the magnetic recording medium. Meanwhile, inthe magnetic tape apparatus, a magnetic tape is used as the magneticrecording medium.

In both of the magnetic disk apparatus and the magnetic tape apparatus,it is preferable to narrow a recording track width, in order to increaserecording capacity (to make high capacity). On the other hand, as therecording track width is narrowed, a signal of an adjacent track iseasily mixed with a signal of a reading target track during thereproducing, and accordingly, it is difficult to maintain reproducingquality in a signal-to-noise ratio (SNR) or the like. In this regard, inrecent years, it is proposed to improve reproducing quality by reading asignal of a recording track by a plurality of reading elements (alsoreferred to as “reproducing elements”) two-dimensionally (for example,see JP2016-110680A, JP2011-134372A, and U.S. Pat. No. 7,755,863B). In acase where the reproducing quality can be improved by doing so, thereproducing quality can be maintained, even in a case where therecording track width is narrowed, and accordingly, it is possible toincrease recording capacity by narrowing the recording track width.

SUMMARY OF THE INVENTION

In JP2016-110680A and JP2011-134372A, studies regarding a magnetic diskapparatus are conducted. Meanwhile, in recent years, a magnetic tape isreceiving attention as a data storage medium for storing a large amountof data for a long period of time. However, the magnetic tape apparatusis generally a sliding type apparatus in which data reading(reproducing) is performed due to contact and sliding between themagnetic tape and a reading element. Accordingly, a relative positionbetween the reading element and a reading target track easily changesduring the reproducing, and the reproducing quality in the magnetic tapeapparatus tends to be hardly improved, compared to that in the magneticdisk apparatus. U.S. Pat. No. 7,755,863B discloses the descriptionregarding the magnetic tape apparatus (tape drive), but does notdisclose specific means for improving the reproducing quality of themagnetic tape apparatus.

An object of an aspect of the present invention is to provide a magnetictape capable of reproducing data with excellent reproducing quality in amagnetic tape apparatus that uses a plurality of reading elements(reproducing elements).

An aspect of the present invention relates to a magnetic tapecomprising: a non-magnetic support; and a magnetic layer includingferromagnetic powder and a binding agent, in which the magnetic layerhas a timing-based servo pattern, an edge shape of the timing-basedservo pattern, specified by magnetic force microscopy is a shape inwhich a difference L_(99.9)−L_(0.1) between a value L_(99.9) of acumulative distribution function of 99.9% and a value L_(0.1) of acumulative distribution function of 0.1% in a position deviation widthfrom an ideal shape of the magnetic tape in a longitudinal direction is180 nm or less, and an absolute value ΔN (hereinafter, also referred toas “ΔN (of magnetic layer)”) of a difference between a refractive indexNxy of the magnetic layer, measured in an in-plane direction and arefractive index Nz of the magnetic layer, measured in a thicknessdirection is 0.25 or more and 0.40 or less.

In an aspect, Nxy>Nz may be satisfied, and a difference (Nxy−Nz) betweenthe refractive index Nxy and the refractive index Nz may be 0.25 or moreand 0.40 or less.

In an aspect, the timing-based servo pattern may be a linear servopattern which continuously extends from one side of the magnetic tape ina width direction to the other side thereof and is inclined at an angleα with respect to the width direction, and the ideal shape may be alinear shape extending in a direction of the angle α.

In an aspect, the difference (L_(99.9)−L_(0.1)) may be 100 nm or moreand 180 nm or less.

In an aspect, the magnetic tape may further comprise a non-magneticlayer including non-magnetic powder and a binding agent between thenon-magnetic support and the magnetic layer.

In an aspect, the magnetic tape may further comprise a back coatinglayer including non-magnetic powder and a binding agent on a surfaceside of the non-magnetic support opposite to a surface side providedwith the magnetic layer.

An aspect of the present invention relates to a magnetic tape cartridgecomprising the above magnetic tape.

An aspect of the present invention relates to a magnetic tape apparatuscomprising: a magnetic tape; a reading element unit; and an extractionunit, in which the magnetic tape is the magnetic tape according to theaspects of the present invention, the reading element unit includes aplurality of reading elements each of which reads data from a specifictrack region including a reading target track in a track region includedin the magnetic tape, and the extraction unit performs a waveformequalization process with respect to each reading result for eachreading element, to extract, from the reading result, data derived fromthe reading target track.

In an aspect, each of the plurality of reading element may read data bya linear scanning method from the specific track region including thereading target track in the track region included in the magnetic tape.

In an aspect, the waveform equalization process may be a waveformequalization process according to a deviation amount in position betweenthe magnetic tape and the reading element unit.

In an aspect, the waveform equalization process may be performed byusing a tap coefficient determined in accordance with the deviationamount.

In an aspect, the deviation amount may be determined in accordance witha result obtained by reading the timing-based servo pattern of themagnetic layer of the magnetic tape using a servo element.

In an aspect, the reading element unit may include a servo element and areading operation by the reading element unit may be performedsynchronously with a reading operation by the servo element.

In an aspect, parts of the plurality of reading elements may beoverlapped each other in a running direction of the magnetic tape.

In an aspect, the specific track region may be a region including thereading target track and an adjacent track which is adjacent to thereading target track, and each of the plurality of reading elements maystraddle over both of the reading target track and the adjacent track,in a case where a positional relationship with the magnetic tape ischanged.

In an aspect, the plurality of reading elements may be disposed in aline in a state of being adjacent to each other, in a width direction ofthe magnetic tape.

In an aspect, the plurality of reading elements may fall in the readingtarget track in a width direction of the magnetic tape.

In an aspect, regarding each of the plurality of reading elements, aratio between an overlapping region with the reading target track and anoverlapping region with an adjacent track which is adjacent to thereading target track may be specified from the deviation amount, and thetap coefficient may be determined in accordance with the specifiedratio.

In an aspect, the extraction unit may include a two-dimensional finiteimpulse response (FIR) filter, and the two-dimensional FIR filter maycompose each result obtained by performing the waveform equalizationprocess with respect to each reading result for each reading element, toextract, from the reading result, data derived from the reading targettrack.

In an aspect, the plurality of reading elements may be a pair of readingelements.

According to an aspect of the present invention, it is possible toprovide a magnetic tape with which a magnetic tape apparatus using aplurality of reading elements (reproducing elements) can reproduce datawith excellent reproducing quality. According to an aspect of thepresent invention, it is possible to provide a magnetic tape cartridgeincluding the magnetic tape. According to an aspect of the presentinvention, it is possible to provide a magnetic tape apparatus includingthe magnetic tape and a plurality of reading elements (reproducingelements).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration view showing an example of an entireconfiguration of a magnetic tape apparatus.

FIG. 2 is a schematic plan view showing an example of a schematicconfiguration in a plan view of a reading head and a magnetic tapeincluded in the magnetic tape apparatus.

FIG. 3 is a schematic plan view showing an example of a schematicconfiguration in a plan view of a reading element unit and the magnetictape.

FIG. 4 is a schematic plan view showing an example of a schematicconfiguration in a plan view of a track region and a reading elementpair.

FIG. 5 is a graph showing an example of a correlation between an SNRregarding each of single reading element data and first composite dataunder a first condition, and track off-set.

FIG. 6 is a graph showing an example of a correlation between an SNRregarding each of single reading element data and second composite dataunder a second condition, and track off-set.

FIG. 7 is a block diagram showing an example of a main configuration ofhardware of an electric system of the magnetic tape apparatus.

FIG. 8 is a conceptual view provided for description of a method ofcalculating a deviation amount.

FIG. 9 is a flowchart showing an example of a flow of a magnetic tapereading process.

FIG. 10 is a conceptual view provided for description of a processperformed by a two-dimensional FIR filter of an extraction unit.

FIG. 11 is a schematic plan view showing an example of a state where thereading element unit straddles over a reading target track and a secondnoise mixing source track.

FIG. 12 is a schematic plan view showing a first modification example ofthe reading element unit.

FIG. 13 is a schematic plan view showing a second modification exampleof the reading element unit.

FIG. 14 shows a disposition example of a data band and a servo band.

FIG. 15 shows a disposition example of a servo pattern of alinear-tape-open (LTO) Ultrium format tape.

FIG. 16 is a view for describing an angle α regarding an edge shape ofthe servo pattern.

FIG. 17 is a view for describing an angle α regarding an edge shape ofthe servo pattern.

FIG. 18 shows an example of the edge shape of the servo pattern.

FIG. 19 shows an example of the servo pattern.

FIG. 20 shows an example of the servo pattern.

FIG. 21 shows an example of the servo pattern.

FIG. 22 is a conceptual view provided for description of a firstexample.

FIG. 23 is a conceptual view provided for description of a secondexample.

FIG. 24 is a view showing an example of a two-dimensional image of areproducing signal obtained from a single reading element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, first, a configuration of a magnetic tape apparatus using aplurality of reading elements (reproducing elements) will be described.

The magnetic tape apparatus includes a magnetic tape, a reading elementunit, and an extraction unit. With respect to reading data from themagnetic tape, in an example shown in FIG. 22, an elongated reading head200 comprises a plurality of reading elements 202 along a longitudinaldirection. In a magnetic tape 204, a plurality of tracks 206 are formed.The reading head 200 is disposed so that the longitudinal directioncoincides with a width direction of the magnetic tape 204. In addition,each of the plurality of reading elements 202 is allocated for each ofthe plurality of tracks 206 in a one-to-one relation, and reads datafrom the track 206 at a position faced.

However, in general, the magnetic tape 204 expands and contracts due totime elapse, an environment, a change of a tension, and the like. In acase where the magnetic tape expands and contracts in a width directionof the magnetic tape 204, the center of each of the reading elements 202disposed on both ends in the longitudinal direction in the reading head200 is deviated from the center of the track 206. In a case where themagnetic tape 204 is deformed due to the expansion and contraction in awidth direction, particularly, the reading elements 202 closer to bothends of the reading head 200, among the plurality of reading elements202, receive a greater effect of off-track. In order to reduce theeffect of the off-track, for example, a method of applying a surpluswidth to the width of the track 206 has been considered. However, as thewidth of the track 206 increases, a recording capacity of the magnetictape 204 decreases.

In addition, as shown in FIG. 23 as an example, in general, a servoelement 208 is provided in the reading head 200. Regarding a magnetictape 204, a servo pattern formed on a magnetic layer of the magnetictape 204 is read by the servo element 208. A control device (not shown)specifies that which position on the magnetic tape 204 the readingelement 202 runs on, for example, at regular time interval, from theservo signal obtained by reading the servo pattern by the servo element208. Accordingly, a position error signal (PES) in a width direction ofthe magnetic tape 204 is detected by the control device.

As described above, in a case where the control device specifies arunning position of the reading element 202, a feedback control isperformed with respect to an actuator (not shown) for the reading headby the control device based on the specified running position, andaccordingly, tracking by the magnetic tape 204 in the width direction isrealized.

However, although the tracking is performed, sharp vibration, ahigh-frequency component of jitter, and the like are factors of anincrease in PES, and this causes a deterioration in reproducing qualityof data read from a reading target track.

On the other hand, in a case where data is each read by the plurality ofreading elements from a specific track region including a reading targettrack in a track region included in the magnetic tape, a waveformequalization process is performed with respect to each reading resultfor each reading element, and data derived from the reading target trackis extracted from the reading result, it is possible to improvereproducing quality of the data read from the reading target track,compared to a case where data is read by only a single reading elementfrom the reading target track. As a result, it is possible to increasean acceptable amount of a deviation amount (a track off-set amount), forensuring excellent reproducing quality.

Here, in a case where a change of the relative position between thereading element and the reading target track (hereinafter, referred toas “relative positional change”) is large, a waveform equalizationprocess performed on each of the reading results for each of theplurality of reading elements may not necessarily be a most suitablewaveform equalization process for each read result. For example, awaveform equalization process performed by a two-dimensional FIR filterdetermined according to the reading result of the servo pattern may notnecessarily be a most suitable waveform equalization process for eachreading result. On the other hand, in a case where the relativepositional change can be suppressed, a more suitable waveformequalization process can be performed for each of the reading resultsread by the plurality of reading elements. As a result, it is possibleto increase an acceptable amount of a deviation amount, for ensuringexcellent reproducing quality with respect to data derived from thereading target track, extracted by performing the waveform equalizationprocess. In this regard, in the magnetic tape according to an aspect ofthe present invention, it is considered that ΔN of the magnetic layer of0.25 or more and 0.40 or less leads to stabilization of a contact statebetween the magnetic tape and the reading element. It is supposed thatthis aspect contributes to suppression of the relative positionalchange. This point will be further described later.

Further, as the servo pattern is formed to be closer to a design shape(for example, ideal shape, details of which will be described later), anaccuracy of specifying the position where the reading element istraveling is higher. This also leads to an increase in an acceptableamount of a deviation amount (a track off-set amount), for ensuringexcellent reproducing quality. In this regard, the difference(L_(99.9)−L_(0.1)) is an index related to a shape of the servo pattern(timing-based servo pattern). Details thereof will be described later.

As described above, an increase in an acceptable amount of a deviationamount, for ensuring excellent reproducing quality can contribute to thereproducing with excellent reproducing quality (for example, high SNR orlow error rate), even in a case where a track margin (recording trackwidth−reproducing element width) is decreased. A decrease in a trackmargin can contribute to an increase in the number of recording trackscapable of being disposed in a width direction of the magnetic tape bydecreasing the recording track width, that is, realization of highcapacity.

Hereinafter, a magnetic tape, a magnetic tape cartridge, and a magnetictape apparatus according to an aspect of the present invention will bedescribed in more detail. In the following, the magnetic tape apparatusand the like may be described with reference to the drawings. However,the present invention is not limited to aspects shown in the drawings.

Configuration of Magnetic Tape Apparatus and Magnetic Tape ReadingProcess

As shown in FIG. 1 as an example, a magnetic tape apparatus 10 comprisesa magnetic tape cartridge 12, a transportation device 14, a reading head16, and a control device 18.

The magnetic tape apparatus 10 is an apparatus which extracts a magnetictape MT from the magnetic tape cartridge 12 and reads data from theextracted magnetic tape MT by using the reading head 16 by a linearscanning method. The reading of data can also be referred to asreproducing of data.

The control device 18 controls the entire magnetic tape apparatus 10. Inan aspect, the control performed by the control device 18 can berealized with an application specific integrated circuit (ASIC). Inaddition, in an aspect, the control performed by the control device 18can be realized with a field-programmable gate array (FPGA). The controlperformed by the control device 18 may be realized with a computerincluding a central processing unit (CPU), a read only memory (ROM), anda random access memory (RAM). Further, the control may be realized witha combination of two or more of AISC, FPGA, and the computer.

The transportation device 14 is a device which selectively transportsthe magnetic tape MT in a forward direction and a backward direction,and comprises a sending motor 20, a winding reel 22, a winding motor 24,a plurality of guide rollers GR, and the control device 18.

A cartridge reel CR is provided in the magnetic tape cartridge 12. Themagnetic tape MT is wound around the cartridge reel CR. The sendingmotor 20 causes the cartridge reel CR in the magnetic tape cartridge 12to be rotatably driven under the control of the control device 18. Thecontrol device 18 controls the sending motor 20 to control a rotationdirection, a rotation rate, a rotation torque, and the like of thecartridge reel CR.

In a case of winding the magnetic tape MT around the winding reel 22,the control device 18 rotates the sending motor 20 so that the magnetictape MT runs in a forward direction. A rotation rate, a rotation torque,and the like of the sending motor 20 are adjusted in accordance with aspeed of the magnetic tape MT wound around the winding reel 22.

The winding motor 24 causes the winding reel 22 to be rotatably drivenunder the control of the control device 18. The control device 18controls the winding motor 24 to control a rotation direction, arotation rate, a rotation torque, and the like of the winding reel 22.

In a case of winding the magnetic tape MT around the winding reel 22,the control device 18 rotates the winding motor 24 so that the magnetictape MT runs in the forward direction. A rotation rate, a rotationtorque, and the like of the winding motor 24 are adjusted in accordancewith a speed of the magnetic tape MT wound around the winding reel 22.

By adjusting the rotation rate, the rotation torque, and the like ofeach of the sending motor 20 and the winding motor 24 as describedabove, a tension in a predetermined range is applied to the magnetictape MT. Here, the predetermined range indicates a range of a tensionobtained from a computer simulation and/or a test performed with a realmachine, as a range of a tension at which data can be read from themagnetic tape MT by the reading head 16, for example.

In a case of rewinding the magnetic tape MT to the cartridge reel CR,the control device 18 rotates the sending motor 20 and the winding motor24 so that the magnetic tape MT runs in the backward direction.

In an aspect, the tension of the magnetic tape MT is controlled bycontrolling the rotation rate, the rotation torque, and the like of eachof the sending motor 20 and the winding motor 24. In addition, in anaspect, the tension of the magnetic tape MT may be controlled by using adancer roller, or may be controlled by drawing the magnetic tape MT to avacuum chamber.

Each of the plurality of guide rollers GR is a roller guiding themagnetic tape MT. A running path of the magnetic tape MT is determinedby separately disposing the plurality of guide rollers GR on positionsstraddling over the reading head 16 between the magnetic tape cartridge12 and the winding reel 22.

The reading head 16 comprises a reading unit 26 and a holder 28. Thereading unit 26 is held by the holder 28 so as to come into contact withthe magnetic tape MT during running.

As shown in FIG. 2 as an example, the magnetic tape MT comprises a trackregion 30 and a servo pattern 32. The servo pattern 32 is a pattern usedfor detection of the position of the reading head 16 on the magnetictape MT. The servo pattern 32 is a pattern in which a first diagonalline 32A at a first predetermined angle (for example, 95 degrees) and asecond diagonal line 32B at a second predetermined angle (for example,85 degrees) are alternately disposed on both end portions in a tapewidth direction at a constant pitch (cycle) along a running direction ofthe magnetic tape MT. The “tape width direction” here indicates a widthdirection of the magnetic tape MT.

The track region 30 is a region where data which is a reading target iswritten, and is formed on the center of the magnetic tape MT in the tapewidth direction. The “center in the tape width direction” hereindicates, for example, a region between the servo pattern 32 on one endportion and the servo pattern 32 on the other end portion of themagnetic tape MT in the tape width direction. Hereinafter, forconvenience of description, the “running direction of the magnetic tapeMT” is simply referred to as the “running direction”.

The reading unit 26 comprises a servo element pair 36 and a plurality ofreading element units 38. The holder 28 is formed to be elongated in thetape width direction, and a total length of the holder 28 in thelongitudinal direction is longer than the width of the magnetic tape MT.The servo element pair 36 is disposed on both end portions of the holder28 in the longitudinal direction, respectively, and the plurality ofreading element units 38 are disposed on the center of the holder 28 inthe longitudinal direction.

The servo element pair 36 comprises servo elements 36A and 36B. Theservo element 36A is disposed on a position facing the servo pattern 32on one end portion of the magnetic tape MT in the tape width direction,and the servo element 36B is disposed on a position facing the servopattern 32 on the other end portion of the magnetic tape MT in the tapewidth direction.

In the holder 28, the plurality of reading element units 38 are disposedbetween the servo element 36A and the servo element 36B along the tapewidth direction. The track region 30 comprises the plurality of tracksat regular interval in the tape width direction, and in a default stateof the magnetic tape apparatus 10, each of the plurality of readingelement units 38 is disposed to face each track in the track region 30.

Accordingly, the reading unit 26 and the magnetic tape MT relativelymove linearly along the longitudinal direction of the magnetic tape MT,and thus, data of each track in the track region 30 is read by eachreading element unit 38 at the corresponding position among theplurality of reading element units 38 by the linear scanning method. Inaddition, in the linear scanning method, the servo patterns 32 are readby the servo element pair 36 synchronously with the reading operation ofthe reading element units 38. That is, in an aspect of the linearscanning method, the reading with respect to the magnetic tape MT isperformed in parallel by the plurality of reading element units 38 andthe servo element pair 36.

Here, “each track in the track region 30” described above indicates atrack included in “each of a plurality of specific track regions eachincluding the reading target track in the track region included in themagnetic tape”.

The “default state of the magnetic tape apparatus 10” indicates a statewhere the magnetic tape MT is not deformed and a positional relationshipbetween the magnetic tape MT head the reading head 16 is a correctpositional relationship. Here, the “correct positional relationship”indicates, for example, a positional relationship in which the center ofthe magnetic tape MT in the tape width direction and the center of thereading head 16 in the longitudinal direction coincide with each other.

In an aspect, each of the plurality of reading element units 38 has thesame configuration. Hereinafter, the description will be performed usingone of the plurality of reading element units 38 as an example, forconvenience of description. As shown in FIG. 3 as an example, thereading element unit 38 comprises a pair of reading elements. In theexample shown in FIG. 3, “a pair of reading elements” indicates a firstreading element 40 and a second reading element 42. Each of the firstreading element 40 and the second reading element 42 reads data from aspecific track region 31 including a reading target track 30A in thetrack region 30.

In the example shown in FIG. 3, for convenience of description, onespecific track region 31 is shown. In practice, in general, in the trackregion 30, a plurality of the specific track regions 31 are present, andthe reading target track 30A is included in each specific track region31. The reading element unit 38 is allocated to each of the plurality ofspecific track regions 31 in a one-to-one manner. Specifically, thereading element unit 38 is allocated to the reading target track 30A ineach of the plurality of specific track regions 31 in a one-to-onemanner.

The specific track region 31 indicates three adjacent tracks. A firsttrack among the three adjacent tracks is the reading target track 30A inthe track region 30. A second track among the three adjacent tracks is afirst noise mixing source track 30B which is one adjacent track adjacentto the reading target track 30A. A third track among the three adjacenttracks is a second noise mixing source track 30C which is one adjacenttrack adjacent to the reading target track 30A. The reading target track30A is a track at a position facing the reading element unit 38 in thetrack region 30. That is, the reading target track 30A indicates a trackhaving data to be read by the reading element unit 38.

The first noise mixing source track 30B is a track which is adjacent tothe reading target track 30A on one side in the tape width direction andis a mixing source of noise mixed to data read from the reading targettrack 30A. The second noise mixing source track 30C is a track which isadjacent to the reading target track 30A on the other side in the tapewidth direction and is a mixing source of noise mixed to data read fromthe reading target track 30A. Hereinafter, for convenience ofdescription, in a case where it is not necessary to describe the firstnoise mixing source track 30B and the second noise mixing source track30C separately, these are referred to as the “adjacent track” withoutreference numerals.

In an aspect, in the track region 30, the plurality of specific trackregions 31 are disposed at regular interval in the tape width direction.For example, in the track region 30, 32 specific track regions 31 aredisposed at regular interval in the tape width direction, and thereading element unit 38 is allocated to each specific track region 31 ina one-to-one manner.

The first reading element 40 and the second reading element 42 aredisposed at positions parts of which are overlapped in the runningdirection, in a state of being adjacent in the running direction. In adefault state of the magnetic tape apparatus 10, the first readingelement 40 is disposed at a position straddling over the reading targettrack 30A and the first noise mixing source track 30B. In a defaultstate of the magnetic tape apparatus 10, the second reading element 42is disposed at a position straddling over the reading target track 30Aand the first noise mixing source track 30B.

In a default state of the magnetic tape apparatus 10, an area of aportion of the first reading element 40 facing the reading target track30A is greater than an area of a portion of the first reading element 40facing the first noise mixing source track 30B, in a plan view.Meanwhile, in a default state of the magnetic tape apparatus 10, an areaof a portion of the second reading element 42 facing the first noisemixing source track 30B is greater than the area of a portion of thefirst reading element 40 facing the reading target track 30A, in a planview.

The data read by the first reading element 40 is subjected to a waveformequalization process by a first equalizer 70 (see FIG. 7) which will bedescribed later. The data read by the second reading element 42 issubjected to a waveform equalization process by a second equalizer 72(see FIG. 7) which will be described later. Each data obtained byperforming the waveform equalization process by each of the firstequalizer 70 and the second equalizer 72 is added by an adder 44 andcomposed.

In FIG. 3, the aspect in which the reading element unit 38 includes thefirst reading element 40 and the second reading element 42 has beendescribed as an example. Here, for example, even in a case where onlyone reading element (hereinafter, also referred to as a single readingelement) among a pair of reading elements is used, a signalcorresponding to a reproducing signal obtained from the reading elementunit 38 is obtained.

In this case, for example, as shown in FIG. 8 as an example, thereproducing signal obtained from the single reading element is allocatedto a plane position on a track calculated from a servo signal obtainedby the servo element pair 36 synchronously with the reproducing signal.By repeating this operation while moving the single reading element inthe tape width direction, a two-dimensional image of the reproducingsignal (hereinafter, simply referred to as a “two-dimensional image”) isobtained. Here, a reproducing signal configuring the two-dimensionalimage or a part of the two-dimensional image (for example, a reproducingsignal corresponding to the positions of the plurality of tracks) is asignal corresponding to the reproducing signal obtained from the readingelement unit 38.

FIG. 24 shows an example of a two-dimensional image of the reproducingsignal obtained by using a loop tester, in the magnetic tape MT in aloop shape (hereinafter, also referred to as a “loop tape”). Here, theloop tester indicates a device which transports the loop tape in a statewhere the loop tape is repeatedly in contact with the single readingelement, for example. In order to obtain a two-dimensional image in thesame manner as in the case of the loop tester, a reel tester may be usedor an actual tape drive may be used. The “reel tester” here indicates adevice which transports the magnetic tape MT in a reel state, forexample.

As described above, even in a case where a head for a magnetic tapewhich does not include the reading element unit on which the pluralityof reading elements are loaded at adjacent positions is used, the effectaccording to the technology disclosed in this specification can bequantitatively evaluated. As an example of an index for quantitativelyevaluating the effect according to the technology disclosed in thisspecification, an SNR, an error rate, and the like are used.

FIGS. 4 to 6 show results obtained from experiments performed by thepresent inventors. As shown in FIG. 4 as an example, a reading elementpair 50 are disposed on a track region 49. The track region 49 includesa first track 49A, a second track 49B, and a third track 49C which areadjacent to one another in the tape width direction. The reading elementpair 50 includes a first reading element 50A and a second readingelement 50B. The first reading element 50A and the second readingelement 50B are disposed at positions adjacent to each other in the tapewidth direction. The first reading element 50A is disposed so as to facethe second track 49B which is the reading target track and fall in thesecond track 49B. In addition, the second reading element 50B isdisposed so as to face the first track 49A adjacent to one side of thesecond track 49B and fall in the first track 49A.

FIG. 5 shows an example of a correlation between an SNR regarding eachof single reading element data and first composite data under a firstcondition, and track off-set. In addition, FIG. 6 shows an example of acorrelation between an SNR regarding each of single reading element dataand second composite data under a second condition, and track off-set.

Here, the single reading element data indicates data obtained byperforming a waveform equalization process with respect to data read bythe first reading element 50A, in the same manner as in the case of thefirst reading element 40 shown in FIG. 3. The first condition indicatesa condition in which a reading element pitch is 700 nm (nanometers). Thesecond condition indicates a condition in which a reading element pitchis 500 nm. The reading element pitch indicates a pitch between the firstreading element 50A and the second reading element 50B in the tape widthdirection, as shown in FIG. 4 as an example. The track off-set indicatesa deviation amount between the center of the second track 49B in thetape width direction and the center of the first reading element 50A inthe track width direction, as shown in FIG. 4 as an example.

The first composite data indicates data composed by adding firstwaveform equalized data and second waveform equalized data obtainedunder the first condition. The first waveform equalized data indicatesdata obtained by performing the waveform equalization process withrespect to the data read by the first reading element 50A, in the samemanner as in the case of the first reading element 40 shown in FIG. 3.The second waveform equalized data indicates data obtained by performingthe waveform equalization process with respect to the data read by thesecond reading element 50B, in the same manner as in the case of thesecond reading element 42 shown in FIG. 3. The second composite dataindicates data composed by adding first waveform equalized data andsecond waveform equalized data obtained under the second condition.

In a case of comparing the SNR of the first composite data shown in FIG.5 to the SNR of the second composite data shown in FIG. 6, the SNR ofthe first composite data rapidly declines to generate a groove of thegraph in a range of the track off-set of −0.4 μm (micrometers) to 0.2μm, whereas the SNR of the second composite data does not rapidlydecline as the graph of the SNR of the first composite data. Each of theSNR of the first composite data and the SNR of the second composite datais higher than the SNR of the single reading element data, andparticularly, the SNR of the second composite data is higher than theSNR of the single reading element data over the entire range of thetrack off-set.

From the experimental results shown in FIGS. 5 and 6, the presentinventors have found that it is preferable to perform the reading ofdata in a state where the first reading element 50A and the secondreading element 50B are adjacent to each other in the tape widthdirection, compared to a case where the reading of data is performed byonly the first reading element 50A. The “state adjacent to each other”here means, for example, that the first reading element 50A and thesecond reading element 50B are not in contact with each other, but aredisposed in a line in the tape width direction, so that the SNR of thecomposite data becomes higher than the SNR of the single reading elementdata, over the entire range of the track off-set.

In an aspect, as shown in FIG. 3 as an example, in the reading elementunit 38, parts of the first reading element 40 and the second readingelement 42 are overlapped each other in the running direction, andaccordingly, a high density of the tracks included in the magnetic tapeMT is realized.

As shown in FIG. 7 as an example, the magnetic tape apparatus 10comprises an actuator 60, an extraction unit 62, analog/digital (A/D)converters 64, 66, and 68, a decoding unit 69, and a computer 73.

The control device 18 is connected to the servo element pair 36 throughthe analog/digital (A/D) converter 68. The A/D converter 68 outputs aservo signal obtained by converting an analog signal obtained by readingthe servo pattern 32 by the servo elements 36A and 36B included in theservo element pairs 36 into a digital signal, to the control device 18.

The control device 18 is connected to the actuator 60. The actuator 60is attached to the reading head 16 and applies power to the reading head16 under the control of the control device 18, to change the position ofthe reading head 16 in the tape width direction. The actuator 60includes, for example, a voice coil motor, and the power applied to thereading head 16 is power obtained by converting an electric energy basedon a current flowing through the coil into a kinetic energy, using anenergy of a magnet as a medium.

Here, the aspect in which the voice coil motor is loaded on the actuator60 has been described. Here, the magnetic tape apparatus is not limitedto the aspect, and for example, a piezoelectric element can also beused, instead of the voice coil motor. In addition, the voice coil motorand the piezoelectric element can be combined with each other.

In an aspect, the deviation amount of the positions of the magnetic tapeMT and the reading element unit 38 is determined in accordance with aservo signal which is a result obtained by reading the servo pattern 32by the servo element pair 36. The control device 18 controls theactuator 60 to apply power according to the deviation amount of thepositions of the magnetic tape MT and the reading element unit 38 to thereading head 16. Accordingly, the position of the reading head 16 ischanged in the tape width direction and the position of the reading head16 is adjusted to a normal position. Here, as shown in FIG. 3, thenormal position indicates, for example, a position of the reading head16 in a default state of the magnetic tape apparatus 10.

Here, the aspect in which the deviation amount of the positions of themagnetic tape MT and the reading element unit 38 is determined inaccordance with the servo signal which is the result obtained by readingthe servo pattern 32 by the servo element pair 36 is used as an example.However, the magnetic tape apparatus according to an aspect of thepresent invention is not limited to such an example. For example, as thedeviation amount of the positions of the magnetic tape MT and thereading element unit 38, the deviation amount from predeterminedreference positions of the servo element 36A and the magnetic tape MTmay be used, or the deviation amount of an end surface of the readinghead 16 and a center position of a specific track included in themagnetic tape MT may be used. As described above, the deviation amountof the positions of the magnetic tape MT and the reading element unit 38may be the deviation amount corresponding to the deviation amountbetween the center of the reading target track 30A in the tape widthdirection and the center of the reading head 16 in the tape widthdirection. Hereinafter, for convenience of description, the deviationamount of the positions of the magnetic tape MT and the reading elementunit 38 is simply referred to as a “deviation amount”.

For example, as shown in FIG. 8, the deviation amount is calculatedbased on a ratio of a distance A to a distance B. The distance Aindicates a distance calculated from a result obtained by reading thefirst diagonal line 32A and the second diagonal line 32B adjacent toeach other by the servo element 36A. The distance B indicates a distancecalculated from a result obtained by reading the two first diagonallines 32A adjacent to each other by the servo element 36A.

The extraction unit 62 comprises the control device 18 and atwo-dimensional FIR filter 71. The two-dimensional FIR filter 71comprises the adder 44, the first equalizer 70, and the second equalizer72.

The first equalizer 70 is connected to the first reading element 40through the A/D converter 64. In addition, the first equalizer 70 isconnected to each of the control device 18 and the adder 44. The dataread by the first reading element 40 from the specific track region 31is an analog signal, and the A/D converter 64 outputs a first readingsignal obtained by converting the data read by the first reading element40 from the specific track region 31 into a digital signal, to the firstequalizer 70.

The second equalizer 72 is connected to the second reading element 42through the A/D converter 66. In addition, the second equalizer 72 isconnected to each of the control device 18 and the adder 44. The dataread by the second reading element 42 from the specific track region 31is an analog signal, and the A/D converter 66 outputs a second readingsignal obtained by converting the data read by the second readingelement 42 from the specific track region 31 into a digital signal, tothe second equalizer 72. Each of the first reading signal and the secondreading signal is an example of a “reading result for each readingelement”.

The first equalizer 70 performs a waveform equalization process withrespect to the input first reading signal. For example, the firstequalizer 70 performs a convolution arithmetic operation of a tapcoefficient with respect to the input first reading signal, and outputsthe first arithmetic operation processed signal which is a signal afterthe arithmetic operation.

The second equalizer 72 performs a waveform equalization process withrespect to the input second reading signal. For example, the secondequalizer 72 performs a convolution arithmetic operation of a tapcoefficient with respect to the input second reading signal, and outputsthe second arithmetic operation processed signal which is a signal afterthe arithmetic operation.

Each of the first equalizer 70 and the second equalizer 72 outputs thefirst arithmetic operation processed signal and the second arithmeticoperation processed signal to the adder 44. The adder 44 adds andcomposes the first arithmetic operation processed signal input from thefirst equalizer 70 and the second arithmetic operation processed signalinput from the second equalizer 72, and outputs the composite dataobtained by the composite to the decoding unit 69.

Each of the first equalizer 70 and the second equalizer 72 is aone-dimensional FIR filter.

In an aspect, the FIR filter is a series of actual values includingpositive and negative values, the number of lines of the series isreferred to as a tap number, and the numerical value is referred to as atap coefficient. In addition, in an aspect, the waveform equalizationindicates a process of the convolution arithmetic operation(multiplication and accumulation) of the series of actual values, thatis, the tap coefficient, with respect to the reading signal. The“reading signal” here indicates a collective term of the first readingsignal and the second reading signal. In an aspect, the equalizerindicates a circuit which carries out a process of performing theconvolution arithmetic operation of the tap coefficient with respect tothe reading signal or the other input signal and outputting the signalafter the arithmetic operation. In addition, in an aspect, the adderindicates a circuit which simply adds two series. Weighting of the twoseries is reflected on the numerical values, that is, the tapcoefficient of the FIR filter used in the first equalizer 70 and thesecond equalizer 72.

The control device 18 performs the waveform equalization processaccording to the deviation amount with respect to each of the firstequalizer 70 and the second equalizer 72 by setting the tap coefficientaccording to the deviation amount with respect to the FIR filter of eachof the first equalizer 70 and the second equalizer 72.

The control device 18 comprises an association table 18A. Theassociation table 18A associates the tap coefficient with the deviationamount regarding each of the first equalizer 70 and the second equalizer72. A combination of the tap coefficient and the deviation amount is,for example, a combination obtained in advance as a combination of thetap coefficient and the deviation amount, with which the best compositedata is obtained by the adder 44, based on the result obtained byperforming at least one of the test performed with a real machine or asimulation. The “best composite data” here indicates data correspondingto the reading target track data.

Here, the “reading target track data” indicates “data derived from thereading target track 30A”. The “data derived from the reading targettrack 30A” indicates data corresponding to data written on the readingtarget track 30A. As an example of data corresponding to the datawritten on the reading target track 30A, data which is read from thereading target track 30A and to which a noise component from theadjacent tracks is not mixed is used.

As described above, the association table 18A is used as an example. Inanother aspect, an arithmetic expression may be used instead of theassociation table 18A. The “arithmetic expression” here indicates anarithmetic expression in which an independent variable is set as thedeviation amount and a dependent variable is set as the tap coefficient,for example.

As described above, the aspect in which the tap coefficient is derivedfrom the association table 18A, in which combinations of the tapcoefficients and the deviation amounts are regulated, has beendescribed. In another aspect, for example, the tap coefficient may bederived from the association table in which the combinations of tapcoefficients and ratios are regulated, or the arithmetic expression. The“ratio” here indicates a ratio between an overlapping region with thereading target track 30A and an overlapping region with the adjacenttrack, regarding each of the first reading element 40 and the secondreading element 42. The ratio is calculated and specified from thedeviation amount by the control device 18 and the tap coefficient isdetermined in accordance with the specified ratio. Alternatively, in anaspect, it is possible to determine a series of a series of a pluralityof the tap coefficients so as to minimize an error from a referencewaveform (target) which is an equalization target using a plurality ofthe reading results obtained by reading data by each of the plurality ofreading elements in a calibration region in advance, for example.

The decoding unit 69 decodes the composite data input from the adder 44and outputs a decoded signal obtained by the decoding to the computer73. The computer 73 performs various processes with respect to thedecoded signal input from the decoding unit 69.

Next, a magnetic tape reading process carried out by the extraction unit62 will be described with reference to FIG. 9. Hereinafter, forconvenience of description, the embodiment is described based onassumption that the servo signal is input to the control device 18, in acase where a period of sampling comes. Here, the sampling is not limitedto the sampling of the servo signal and also means the sampling of thereading signal. That is, in an aspect, the track region 30 is formed inparallel with the servo pattern 32 along the running direction, andaccordingly, the reading operation by the reading element unit 38 isperformed synchronously with the reading operation by the servo elementpair 36.

In the process shown in FIG. 9, first, in a step S100, the controldevice 18 determines whether or not the period of the sampling comes. Inthe step S100, in a case where the period of the sampling comes, thedetermination is affirmative and the magnetic tape reading process movesto a step S102. In the step S100, in a case where the period of thesampling does not come, the determination is denied, and thedetermination of the step S100 is performed again.

In a step S102, the first equalizer 70 acquires a first reading signal,the second equalizer 72 acquires a second reading signal, and then, themagnetic tape reading process moves to a step S104.

In the step S104, the control device 18 acquires a servo signal andcalculates a deviation amount from the acquired servo signal, and thenthe magnetic tape reading process moves to a step S106.

In the step S106, the control device 18 derives a tap coefficientcorresponding to the deviation amount calculated in the process of thestep S104 from the association table 18A, regarding first to third tapsof each of the first equalizer 70 and the second equalizer 72. That is,by performing the process of the step S106, an optimal combination isdetermined as a combination of a one-dimensional FIR filter which is anexample of the first equalizer 70 and a one-dimensional filter which isan example of the second equalizer 72. The “optimal combination” hereindicates, for example, a combination in which the composite data outputby performing a process of a step S112 which will be described later isset as data corresponding to the reading target track data.

In the next step S108, the control device 18 sets the tap coefficientderived in the process of the step S106 with respect to each of thefirst equalizer 70 and the second equalizer 72, and then the magnetictape reading process moves to a step S110.

In the step S110, the first equalizer 70 performs the waveformequalization process with respect to the first reading signal acquiredin the process of the step S102, and accordingly, the first arithmeticoperation processed signal is generated. The first equalizer 70 outputsthe generated first arithmetic operation processed signal to the adder44. The second equalizer 72 performs the waveform equalization processwith respect to the second reading signal acquired in the process of thestep S102, and accordingly, the second arithmetic operation processedsignal is generated. The second equalizer 72 outputs the generatedsecond arithmetic operation processed signal to the adder 44.

In the next step S112, the adder 44 adds and composes the firstarithmetic operation processed signal input from the first equalizer 70and the second arithmetic operation processed signal input from thesecond equalizer 72, as shown in FIG. 10 as an example. The adder 44outputs the composite data obtained by the composite to the decodingunit 69.

In a case where the reading element unit 38 is disposed in the specifictrack region 31, as the example shown in FIG. 3, the data correspondingto the reading target track data, from which the noise component fromthe first noise mixing source track 30B is removed, is output as thecomposite data, by performing the process of the step S112. That is, byperforming the processes of the step S102 to the step S112, theextraction unit 62 extracts only the data derived from the readingtarget track 30A.

In a case where the magnetic tape MT expands and contracts in the tapewidth direction or vibration is applied to at least one of the magnetictape MT or the reading head 16, the reading element unit 38 is displacedto a position shown in FIG. 11 from the position shown in FIG. 3 as anexample. In the example shown in FIG. 11, the first reading element 40and the second reading element 42 are disposed at positions straddlingover both of the reading target track 30A and the second noise mixingsource track 30C. In this case, by performing the processes of the stepS102 to the step S112, the data corresponding to the reading targettrack data, from which the noise component from the second noise mixingsource track 30C is removed, is output to the decoding unit 69 as thecomposite data.

In the next step S114, the control device 18 determines whether or not acondition for completing the magnetic tape reading process (hereinafter,referred to as a “completion condition”) is satisfied. The completioncondition indicates, for example, a condition in which the entiremagnetic tape MT is wound around the winding reel 22, a condition inwhich an instruction for forced completion of the magnetic tape readingprocess is applied from the outside, and the like.

In the step S114, in a case where the completion condition is notsatisfied, the determination is denied, and the magnetic tape readingprocess is moved to the step S100. In the step S114, in a case where thecompletion condition is satisfied, the determination is affirmative, andthe magnetic tape reading process ends.

As described above, in an aspect of the magnetic tape apparatus 10, thedata is read from the specific track region 31 by each of the firstreading element 40 and the second reading element 42 disposed in a stateof being adjacent to each other. In addition, the extraction unit 62performs the waveform equalization process according to the deviationamount with respect to each of the first reading element 40 and thesecond reading element 42, to extract the data derived from the readingtarget track 30A from the first reading signal and the second readingsignal. Therefore, in the magnetic tape apparatus 10, it is possible toprevent a deterioration in reproducing quality of data read from thereading target track 30A by the linear scanning method, compared to acase where the data is read from the reading target track 30A by only asingle reading element by the linear scanning method.

In an aspect of the magnetic tape apparatus 10, parts of the firstreading element 40 and the second reading element 42 are overlapped eachother in the running direction. Therefore, in the magnetic tapeapparatus 10, it is possible to increase reproducing quality of dataread from the reading target track 30A by the linear scanning method,compared to a case where the entire portions of the plurality of readingelements are overlapped in the running direction.

In an aspect of the magnetic tape apparatus 10, the specific trackregion 31 includes the reading target track 30A, the first noise mixingsource track 30B, and the second noise mixing source track 30C, and eachof the first reading element 40 and the second reading element 42straddles over both of the reading target track 30A and the adjacenttrack, in a case where a positional relationship with the magnetic tapeMT is changed. Therefore, in the magnetic tape apparatus 10, it ispossible to reduce the noise component generated in one of the readingelement of the first reading element 40 and the second reading element42 due to entering the adjacent track from the reading target track 30Ain the tape width direction, by using the reading result obtained by theother reading element entering the adjacent track from the readingtarget track 30A in the tape width direction, compared to a case wherethe data is read by only the single reading element from the readingtarget track 30A.

In an aspect of the magnetic tape apparatus 10, the tap coefficient usedin the waveform equalization process is determined in accordance withthe deviation amount. Therefore, by determining the tap coefficient inaccordance with the deviation amount, it is possible to instantaneouslyreduce the noise component generated due to entering the reading targettrack 30A from the adjacent track in the tape width direction, inaccordance with a change of the positional relationship between themagnetic tape MT and the reading element unit 38, compared to a casewhere the tap coefficient is determined in accordance with a parameterwith no relation with the deviation amount.

In an aspect of the magnetic tape apparatus 10, regarding each of thefirst reading element 40 and the second reading element 42, the ratiobetween the overlapping region with the reading target track 30A and theoverlapping region with the adjacent track is specified from thedeviation amount, and the tap coefficient is determined according to thespecified ratio. Therefore, in the magnetic tape apparatus 10, it ispossible to exactly reduce the noise component, even in a case where thepositional relationship between the magnetic tape MT and the readingelement unit 38 is changed, compared to a case where the tap coefficientis determined in accordance with a parameter with no relation with aratio between the overlapping region with the reading target track 30Aand the overlapping region with the adjacent track regarding each of theplurality of reading elements.

In an aspect of the magnetic tape apparatus 10, the deviation amount isdetermined in accordance with the result obtained by reading the servopatterns 32 by the servo element pair 36. Therefore, in the magnetictape apparatus 10, it is possible to easily determine the deviationamount, compared to a case where the servo patterns 32 are not appliedto the magnetic tape MT.

In an aspect of the magnetic tape apparatus 10, the reading operation bythe reading element unit 38 is performed synchronously with the readingoperation by the servo element pair 36. Therefore, in the magnetic tapeapparatus 10, it is possible to instantaneously reduce the noisecomponent generated due to entering the reading target track from theadjacent track in the width direction of the magnetic tape, compared toa case of a magnetic disk and a magnetic tape in a helical scanningmethod, in which a servo pattern and data cannot be synchronously read.

In an aspect of the magnetic tape apparatus 10, the extraction unit 62includes the two-dimensional FIR filter 71. Each result obtained byperforming the waveform equalization process with respect to each of thefirst reading signal and the second reading signal is composed by thetwo-dimensional FIR filter 71, and accordingly, the data derived fromthe reading target track 30A is extracted from the first reading signaland the second reading signal. Therefore, in the magnetic tape apparatus10, it is possible to rapidly extract the data derived from the readingtarget track 30A from the first reading signal and the second readingsignal, compared to a case of using only a one-dimensional FIR filter.In addition, in the magnetic tape apparatus 10, it is possible torealize an operation due to a smaller operation amount, compared to acase of performing a matrix operation.

In an aspect of the magnetic tape apparatus 10, the first readingelement 40 and the second reading element 42 are used as a pair ofreading elements. Therefore, in the magnetic tape apparatus 10, it ispossible to contribute to miniaturization of the reading element unit38, compared to a case of using three or more reading elements. Byminiaturizing the reading element unit 38, the reading unit 26 and thereading head 16 can also be miniaturized. In addition, in the magnetictape apparatus 10, it is also possible to prevent occurrence of asituation in which the reading element units 38 adjacent to each otherare in contact with each other.

In an aspect of the magnetic tape apparatus 10, each of the plurality ofreading element units 38 reads data from the corresponding readingtarget track 30A included in each of the plurality of specific trackregions 31 by the linear scanning method. Therefore, in the magnetictape apparatus 10, it is possible to rapidly complete the reading ofdata from the plurality of reading target tracks 30A, compared to a casewhere the data is read by only the single reading element unit 38 fromeach of the plurality of reading target tracks 30A.

In the aspect, in a default state of the magnetic tape apparatus 10,each of the first reading element 40 and the second reading element 42is provided to straddle over both of the reading target track 30A andthe first noise mixing source track 30B, here, the magnetic tapeapparatus is not limited to the aspect. In an example shown in FIG. 12,a reading element unit 138 is used instead of the reading element unit38 described above. The reading element unit 138 comprises a firstreading element 140 and a second reading element 142. In a default stateof the magnetic tape apparatus 10, the center of the first readingelement 140 in the tape width direction coincides with a center CL ofthe reading target track 30A in the tape width direction. In a defaultstate of the magnetic tape apparatus 10, the first reading element 140and the second reading element 142 fall in the reading target track 30A,without being protruded to the first noise mixing source track 30B andthe second noise mixing source track 30C. In addition, in a defaultstate of the magnetic tape apparatus 10, parts of the first readingelement 140 and the second reading element 142 are provided to beoverlapped each other in the running direction, in the same manner asthe case of the first reading element 40 and the second reading element42 described in the embodiment.

As shown in FIG. 12 as an example, even in a state where the firstreading element 140 and the second reading element 142 face the readingtarget track 30A, without being protruded from the reading target track30A, a positional relationship between the reading element unit 138 andthe magnetic tape MT may be changed. That is, the reading element unit138 may straddle over the reading target track 30A and the first noisemixing source track 30B, or the reading element unit 138 may straddleover the reading target track 30A and the second noise mixing sourcetrack 30C. Even in these cases, by performing the processes in the stepS102 to the step S112 described above, it is possible to obtain the datacorresponding to the reading target track data, from which the noisecomponent from the first noise mixing source track 30B or the secondnoise mixing source track 30C is removed.

In addition, the first reading element 140 and the second readingelement 142 are disposed at position where parts thereof are overlappedeach other in the running direction, and accordingly, the second readingelement 142 can read the data from a portion of the reading target track30A where the reading cannot be performed by the first reading element140. As a result, it is possible to increase reliability of the readingtarget track data, compared to a case where the first reading element140 singly reads the data from the reading target track 30A.

As shown in FIG. 11 as an example, in a default state of the magnetictape apparatus 10, each of the first reading element 40 and the secondreading element 42 may be disposed at a position straddling over both ofthe reading target track 30A and the second noise mixing source track30C.

As described above, the reading element unit 38 including the firstreading element 40 and the second reading element 42 has been described.However, the magnetic tape apparatus is not limited to the aspect. In anexample shown in FIG. 13, a reading element unit 238 may be used insteadof the reading element unit 38. The reading element unit 238 isdifferent from the reading element unit 38, in a point that a thirdreading element 244 is included. In a default state of the magnetic tapeapparatus 10, the third reading element 244 is disposed at a positionwhere a part thereof is overlapped with a part of the first readingelement 40 in the running direction. In addition, in a default state ofthe magnetic tape apparatus 10, the third reading element 244 isdisposed at a position to straddle over the reading target track 30A andthe second noise mixing source track 30C.

In this case, a third equalizer (not shown) is also allocated to thethird reading element 244, in the same manner as a case where the firstequalizer 70 is allocated to the first reading element 40 and the secondequalizer 72 is allocated to the second reading element 42. The thirdequalizer also has the same function as that of each of the firstequalizer and the second equalizer described above, and performs awaveform equalization process with respect to a third reading signalobtained by reading performed by the third reading element 244. Thethird equalizer performs, for example, a convolution arithmeticoperation of a tap coefficient with respect to the third reading signaland outputs the third arithmetic operation processed signal which is asignal after the arithmetic operation. The adder 44 adds and composes afirst arithmetic operation processed signal corresponding to the firstreading signal, a second arithmetic operation processed signalcorresponding to the second reading signal, the third arithmeticoperation processed signal corresponding to the third reading signal,and outputs the composite data obtained by the composite to the decodingunit 69.

In the example shown in FIG. 13, in a default state of the magnetic tapeapparatus 10, the third reading element 244 is disposed at the positionstraddling over the reading target track 30A and the second noise mixingsource track 30C, but the technology of the present disclosure is notlimited thereto. In a default state of the magnetic tape apparatus 10,the third reading element 244 may be disposed at the position facing thereading target track 30A, without being protruded from the readingtarget track 30A.

As described above, the reading element unit 38 has been described.However, the magnetic tape apparatus is not limited to the aspect. Forexample, the reading element pair 50 shown in FIG. 4 may be used insteadof the reading element unit 38. In this case, the first reading element50A and the second reading element 50B are set to be disposed atpositions adjacent to each other in the tape width direction. Inaddition, the first reading element 50A and the second reading element50B are set to be disposed in a line in the tape width direction so thatthe SNR of the composite data is higher than the SNR of the singlereading element data over the entire range of the track off-set, asshown in FIG. 6 as an example, without being in contact with each other.

In the example shown in FIG. 4, for example, the first reading element50A falls in the second track 49B in a plan view, and the second readingelement 50B falls in the first track 49A in a plan view.

As described above, the servo element pair 36 has been described.However, the magnetic tape apparatus is not limited to the aspect. Forexample, one of the servo elements 36A and 36B may be used instead ofthe servo element pair 36.

As described above, the aspect in which the plurality of specific trackregions 31 are arranged in the track region 30 at regular interval inthe tape width direction has been described. However, the magnetic tapeapparatus is not limited to the aspect. For example, in two specifictrack regions 31 adjacent to each other in the plurality of specifictrack regions 31, one specific track region 31 and the other specifictrack region 31 may be arranged in the tape width direction so as to beoverlapped by the area of one track in the tape width direction. In thiscase, one adjacent track included in one specific track region 31 (forexample, the first noise mixing source track 30B) becomes the readingtarget track 30A in the other specific track region 31. In addition, thereading target track 30A included in one specific track region 31becomes the adjacent track region (for example, the second noise mixingsource track 30C) in the other specific track region 31.

The configuration of the magnetic tape apparatus and the magnetic tapereading process described above are merely an example. Accordingly,unnecessary steps can be removed, new steps can be added, and theprocess procedure can be changed, within a range not departing from thegist.

The magnetic tape apparatus can perform the reading (reproducing) ofdata recorded on the magnetic tape, and can also have a configurationfor recording data on the magnetic tape.

Magnetic Tape

Next, the details of a magnetic tape according to an aspect of thepresent invention will be described.

The magnetic tape according to the aspect of the present invention has anon-magnetic support; and a magnetic layer including ferromagneticpowder and a binding agent. The magnetic layer has a timing-based servopattern, an edge shape of the timing-based servo pattern, specified bymagnetic force microscopy is a shape in which a difference(L_(99.9)−L_(0.1)) between a value L_(99.9) of a cumulative distributionfunction of 99.9% and a value L_(0.1) of a cumulative distributionfunction of 0.1% in a position deviation width from an ideal shape ofthe magnetic tape in a longitudinal direction is 180 nm or less, and anabsolute value ΔN of a difference between a refractive index Nxy of themagnetic layer, measured in an in-plane direction and a refractive indexNz of the magnetic layer, measured in a thickness direction is 0.25 ormore and 0.40 or less.

In recent years, a timing-based servo type has been widely used as asystem that uses a head tracking servo using a servo signal(hereinafter, referred to as a “servo system”). In the servo system of atiming-based servo type (hereinafter, referred to as a “timing-basedservo system”), a plurality of servo patterns having two or moredifferent shapes are formed on the magnetic layer, and a servo elementrecognizes a position of the servo element based on time interval atwhich two servo patterns having different shapes are reproduced (read)and time interval at which two servo patterns having the same shape arereproduced.

The “timing-based servo pattern” in the present invention and thisspecification refers to a servo pattern in which head tracking ispossible in the timing-based servo system. A servo pattern in which headtracking is possible in the timing-based servo system, as a plurality ofservo patterns having two or more different shapes, is formed on themagnetic layer by a servo write head that is a head for forming theservo pattern. In an example, the plurality of servo patterns having twoor more different shapes are continuously disposed at constant intervalfor each of the plurality of servo patterns having the same shape. Inanother example, different types of servo patterns are alternatelydisposed. Regarding the servo patterns having the same shape, positiondeviation in an edge shape of the servo patterns is ignored. The shapeof the servo pattern in which head tracking is possible in thetiming-based servo system and the disposition on the servo band areknown, and a specific aspect will be described later. Hereinafter, thetiming-based servo pattern is also simply referred to as a servopattern. In the present invention and this specification, an edge shapeof the timing-based servo pattern, specified by magnetic forcemicroscopy is also referred to as a shape of an edge (end side) locatedon a downstream side in a magnetic tape running direction (hereinafter,referred to simply as a “running direction”) in a case where data(information) is recorded.

Next, in the present invention and in the present specification, an edgeshape of the timing-based servo pattern, specified by magnetic forcemicroscopy, a difference (L_(99.9)−L_(0.1)) between a value L_(99.9) ofa cumulative distribution function of 99.9% and a value L_(0.1) of acumulative distribution function of 0.1% in a position deviation widthof the edge shape from an ideal shape of the magnetic tape in alongitudinal direction, and an ideal shape will be described.

Hereinafter, a linear servo pattern that continuously extends from oneside toward the other side of the magnetic tape in a width direction andis inclined at an angle α with respect to a width direction of themagnetic tape will be mainly described as an example. The angle α refersto an angle formed by a line segment connecting two end portions in atape width direction of the edge of the servo pattern located on adownstream side with respect to a running direction of the magnetic tapein a case where data (information) is recorded, and a width direction ofthe magnetic tape. This will be further described below including thispoint.

For example, in a magnetic tape applied in a linear scanning methodwidely used as a recording method of the magnetic tape apparatus, ingeneral, a plurality of regions in each of which a servo pattern isformed (referred to as a “servo band”) exist on the magnetic layer alonga longitudinal direction of the magnetic tape. A region interposedbetween two servo bands is referred to as a data band. The recording ofinformation (magnetic signal) is performed on the data band, and aplurality of data tracks are formed on each data band along alongitudinal direction. FIG. 14 shows a disposition example of a databand and a servo band. In FIG. 14, in the magnetic layer of the magnetictape MT, a plurality of servo bands 1 are disposed between the guidebands 3. A plurality of regions 2 each of which is interposed betweentwo servo bands are data bands. The servo pattern is a magnetizationregion, and is formed by magnetizing a specific region of the magneticlayer with the servo write head. A region magnetized by the servo writehead (a position where the servo pattern is formed) is determined by thestandard. For example, in an LTO Ultrium format tape which is based on alocal standard, a plurality of servo patterns tilted with respect to atape width direction as shown in FIG. 15 are formed on a servo band, ina case of manufacturing a magnetic tape. Specifically, in FIG. 15, aservo frame SF on the servo band 1 is configured with a servo sub-frame1 (SSF1) and a servo sub-frame 2 (SSF2). The servo sub-frame 1 isconfigured with an A burst (in FIG. 15, reference numeral A) and a Bburst (in FIG. 15, reference numeral B). The A burst is configured withservo patterns A1 to A5 and the B burst is configured with servopatterns B1 to B5. Meanwhile, the servo sub-frame 2 is configured with aC burst (in FIG. 15, reference numeral C) and a D burst (in FIG. 15,reference numeral D). The C burst is configured with servo patterns C1to C4 and the D burst is configured with servo patterns D1 to D4. Such18 servo patterns are disposed in the sub-frames in the arrangement of5, 5, 4, 4, as the sets of 5 servo patterns and 4 servo patterns, andare used for recognizing the servo frames. Although one servo frame isshown in FIG. 15, a plurality of servo frames are disposed in each servoband in a running direction. In FIG. 15, an arrow shows a runningdirection. A running direction side of the arrow is an upstream side,and the opposite side is a downstream side.

FIGS. 16 and 17 are views for describing an angle α. In the servopattern shown in FIG. 15, in the servo pattern that is inclined towardan upstream side in a running direction like servo patterns A1 to A5 andC1 to C4, an angle formed by a line segment connecting two end portionsof a downstream edge E_(L) (a broken line L1 in FIG. 16) and a tapewidth direction (a broken line L2 in FIG. 16) is defined as an angle α.On the other hand, in the servo pattern that is inclined toward adownstream side in a running direction like servo patterns B1 to B5 andD1 to D4, an angle formed by a line segment connecting two end portionsof a downstream edge E_(L) (a broken line L1 in FIG. 17) and a tapewidth direction (a broken line L2 in FIG. 17) is defined as an angle α.This angle α is generally referred to as an azimuth angle and isdetermined by the setting of the servo write head in a case of forming amagnetization region (servo pattern) on the servo band.

In a case where the magnetization region (servo pattern) is formed on aservo band, in a case where the servo pattern is ideally formed, an edgeshape of the servo pattern inclined at an angle α with respect to themagnetic tape width direction coincides with a shape of a line segmentconnecting the two end portions of the edge (a broken line L1 in FIGS.16 and 17). That is, the shape becomes a straight line. Therefore, ateach portion on the edge, the positional deviation width from the idealshape of the magnetic tape in a longitudinal direction (hereinafter,also simply referred to as “positional deviation width”) becomes zero.On the other hand, as shown in an example in FIG. 18, an edge shape ofthe servo pattern may deviate from the ideal shape. The difference(L_(99.9)−L_(0.1)) is a value to be an index that the position deviationwidth from the ideal shape is small at each edge position of the servopattern and that variation in the position deviation width at each edgeportion is small. The difference (L_(99.9)−L_(0.1)) is a value obtainedby the following method.

A magnetic layer surface of the magnetic tape on which the servo patternis formed is observed with a magnetic force microscope (MFM). Ameasurement range is a range including five servo patterns. For example,in an LTO Ultrium format tape, five servo patterns of the A burst or theB burst can be observed by setting the measurement range to 90 μm×90 μm.A servo pattern (magnetization region) is extracted by measuring themeasurement range at a 100 nm pitch (rough measurement). In the presentinvention and this specification, the “magnetic layer surface” isidentical to a surface of the magnetic tape on a magnetic layer side.

Thereafter, in order to detect a boundary between the magnetizationregion and the non-magnetization region at the edge of the servo patternlocated on a downstream side with respect to a running direction, amagnetic profile is obtained by performing measurement at a 5 nm pitchin the vicinity of the boundary. In a case where the obtained magneticprofile is inclined at an angle α with respect to a width direction ofthe magnetic tape, the magnetic profile is rotationally corrected byanalysis software so as to be along the magnetic tape width direction(α=0°). Thereafter, position coordinates of a peak value of each profilemeasured at a 5 nm pitch are calculated by analysis software. Theposition coordinates of this peak value indicate a position of aboundary between the magnetization region and the non-magnetizationregion. The position coordinates are specified by, for example, an xycoordinate system in which a running direction is an x coordinate and awidth direction is a y coordinate.

In an example of a case where the ideal shape is a straight line andposition coordinates of a certain position on the straight line are (x,y)=(a, b), in a case where the edge shape actually obtained (positioncoordinates of the boundary) is coincident with an ideal shape, thecalculated position coordinates are (x, y)=(a, b). In this case, apositional deviation width is zero. On the other hand, in a case wherethe edge shape actually obtained is deviated from an ideal shape, thex-coordinate of the position of y=b of the boundary is x=a+c or x=a−c.x=a+c is, for example, a case where a width c is deviated on an upstreamside with respect to a running direction, and x=a−c is, for example, acase where a width c is deviated on a downstream side with respect to arunning direction (that is, −c on the basis of the upstream side). Here,c is a position deviation width. That is, an absolute value of aposition deviation width of the x coordinate from an ideal shape is aposition deviation width from the ideal shape of the magnetic tape inthe longitudinal direction. Thus, a position deviation width at eachedge portion on a downstream side of the running direction of themagnetic profile obtained by measurement at 5 nm pitch is obtained.

From the values obtained for each servo pattern, the cumulativedistribution function is obtained by analysis software. From theobtained cumulative distribution function, the value L_(99.9) of acumulative distribution function of 99.9% and the value L_(0.1) of acumulative distribution function of 0.1% are obtained, and a difference(L_(99.9)−L_(0.1)) is obtained for each servo pattern from the obtainedvalues.

The above measurement is performed in three different measurement ranges(the number of measurements N=3).

An arithmetic average of differences (L_(99.9)−L_(0.1)) obtained foreach servo pattern is defined as the above difference (L_(99.9)−L_(0.1))for the magnetic tape.

The “ideal shape” of an edge shape of the servo pattern in the presentinvention and this specification refers to an edge shape in a case wherethe servo pattern is formed without positional deviation. For example,in an aspect, the servo pattern is a linear servo pattern extendingcontinuously or discontinuously from one side toward the other side ofthe magnetic tape in a width direction. The “linear” for the servopattern refers to that the pattern shape does not include a curvedportion regardless of position deviation of the edge shape. “Continuous”refers to extending from one side toward the other side in a tape widthdirection without an inflection point of a tilt angle and withoutinterruption. An example of the servo pattern extending continuouslyfrom one side toward the other side of the magnetic tape in a widthdirection is a servo pattern shown in FIG. 15. On the other hand,“discontinuous” refers to that there is one or more inflection points ofa tilt angle and/or extending interruptedly at one or more portions. Theshape that extends without interruption even though there is aninflection point of the tilt angle is a so-called polygonal line shape.An example of the discontinuous servo pattern extending from one sidetoward the other side in a tape width direction with one inflectionpoint of the tilt angle and without interruption is a servo patternshown in FIG. 19. On the other hand, an example of the discontinuousservo pattern extending from one side toward the other side in a tapewidth direction without an inflection point of the tilt angle and withinterruption at one portion is a servo pattern shown in FIG. 20. Inaddition, an example of the discontinuous servo pattern extending fromone side toward the other side in a tape width direction with oneinflection point of the tilt angle and with interruption at one portionis a servo pattern shown in FIG. 21.

In a linear servo pattern that continuously extends from one side towardthe other side in a tape width direction, the “ideal shape” of the edgeshape is a shape of a line segment connecting two end portions of anedge on a downstream side in a running direction of the linear servopattern (a linear shape). For example, the linear servo pattern shown inFIG. 15 has a shape of a straight line indicated by L1 in FIG. 16 or 17.On the other hand, in a linear servo pattern that extendsdiscontinuously, the ideal shape is a shape of a line segment connectingone end and the other end of a portion with the same tilt angle (alinear shape) in a shape with an inflection point of a tilt angle. Inaddition, in the shape extending with interruption at one or moreportions, the ideal shape is a shape of a line segment connecting oneend and the other end of each continuously extending portion (linearshape). For example, in the servo pattern shown in FIG. 19, the idealshape is a shape of a line segment connecting e1 and e2, and a linesegment connecting e2 and e3. In the servo pattern shown in FIG. 20, theideal shape is a shape of a line segment connecting e4 and e5, and aline segment connecting e6 and e7. In the servo pattern shown in FIG.21, the ideal shape is a shape of a line segment connecting e8 and e9,and a line segment connecting e10 and e11.

In the above, a linear servo pattern has been described as an example.Here, the servo pattern may be a servo pattern in which an ideal shapeof the edge shape is a curved shape. For example, in a servo pattern inwhich an edge shape on a downstream side with respect to a runningdirection is ideally a partial arc shape, it is possible to obtain adifference (L_(99.9)−L_(0.1)) from a position deviation width, of anedge shape on a downstream side with respect to a running direction,obtained from the position coordinates obtained by a magnetic forcemicroscope, with respect to position coordinates of this partial arc.

As a magnetic force microscope used in the above measurement, acommercially available or known magnetic force microscope is used in afrequency modulation (FM) mode. As a probe of a magnetic forcemicroscope, for example, SSS-MFMR (nominal curvature radius 15 nm)manufactured by Nanoworld AG can be used. A distance between a magneticlayer surface and a probe distal end during magnetic force microscopy isin a range of 20 to 50 nm.

In addition, as analysis software, commercially available analysissoftware or analysis software in which a known arithmetic expression isincorporated can be used.

Next, in the present invention and this specification, an absolute valueΔN of a difference between a refractive index Nxy of the magnetic layer,measured in an in-plane direction and a refractive index Nz of themagnetic layer, measured in a thickness direction is a value obtained bythe following method. In the present invention and this specification,the “magnetic layer surface” is identical to a surface of the magnetictape on a magnetic layer side.

A refractive index of the magnetic layer in each direction is obtainedby a spectral ellipsometry using a two-layer model. In order to obtain arefractive index of the magnetic layer by a spectral ellipsometry usinga two-layer model, a value of a refractive index of a portion adjacentto the magnetic layer is used. Hereinafter, a case of obtainingrefractive indexes Nxy and Nz of the magnetic layer in a magnetic tapehaving a layer configuration in which a non-magnetic layer and amagnetic layer are stacked on a non-magnetic support in this order willbe described as an example. Here, the magnetic tape according to anaspect of the present invention may also be a magnetic tape having alayer configuration in which a magnetic layer is directly stacked on anon-magnetic support without the non-magnetic layer interposedtherebetween. In the magnetic tape having such a configuration, arefractive index of the magnetic layer in each direction is obtainedusing a two-layer model of a magnetic layer and a non-magnetic supportin the same manner as the following method. Moreover, an incidence angledescribed below is an incidence angle in a case where an incident anglein a case of normal incidence is 0°.

(1) Preparation of Measurement Sample

In a magnetic tape having a back coating layer on a surface opposite toa surface having a magnetic layer of a non-magnetic support, measurementis performed after the back coating layer of a measurement sample, cutout from the magnetic tape is removed. The back coating layer can beremoved by a known method such as dissolving the back coating layerusing a solvent. As the solvent, for example, methyl ethyl ketone can beused. Here, any solvent that can remove the back coating layer may beused. A surface of the non-magnetic support after the back coating layeris removed is roughened by a known method so that a reflection ray onthe surface is not detected in the measurement with an ellipsometer.Roughening can be performed by a known method such as polishing asurface of the non-magnetic support after removal of the back coatinglayer using sand paper, for example. In a measurement sample cut outfrom the magnetic tape having no back coating layer, a surface of thenon-magnetic support opposite to a surface having the magnetic layer isroughened.

Further, in order to measure a refractive index of the non-magneticlayer described below, the magnetic layer is further removed to expose anon-magnetic layer surface. In order to measure a refractive index ofthe non-magnetic support described below, the non-magnetic layer isfurther removed to expose a surface of the non-magnetic support on themagnetic layer side. The removal of each layer can be performed by aknown method as described for the removal of the back coating layer. Alongitudinal direction described below refers to a direction that is alongitudinal direction of the magnetic tape in a case where each layeris included in the magnetic tape before a measurement sample is cut out.This is also applied to the other directions described below.

(2) Refractive Index Measurement of Magnetic Layer

Δ (a phase difference between an s-polarized ray and a p-polarized ray)and ψ (an amplitude ratio between an s-polarized ray and a p-polarizedray) are measured, using an ellipsometer, by setting an incidence angleto 65°, 70°, and 75° and irradiating a magnetic layer surface with anincidence ray having a beam diameter of 300 μm in a longitudinaldirection. The measurement is performed by changing a wavelength of anincidence ray by every 1.5 nm in a range of 400 to 700 nm, and ameasurement value is obtained for each wavelength.

A refractive index of a magnetic layer in each wavelength is obtained bya two-layer model as described below, using measurement values of A andw of the magnetic layer in each wavelength, a refractive index of thenon-magnetic layer in each direction obtained by the following method,and a thickness of the magnetic layer.

A 0th layer, which is a substrate of the two-layer model, is anon-magnetic layer, and a first layer is a magnetic layer. Consideringonly reflection at interfaces between air/a magnetic layer and amagnetic layer/a non-magnetic layer, and assuming that there is noinfluence of back surface reflection of the non-magnetic layer, thetwo-layer model is created. A refractive index of the first layer thatmost closely matches the obtained measurement value is obtained byfitting the measurement value by a least squares method. As a value at awavelength of 600 nm, obtained from the fitting result, a refractiveindex Nx of the magnetic layer in a longitudinal direction and arefractive index Nz₁ of the magnetic layer in a thickness direction,measured by making an incidence ray incident in a longitudinal directionare obtained.

In the same manner as the above except that a direction in which anincidence ray is incident is set as a width direction of the magnetictape, as a value at the wavelength of 600 nm obtained from the fittingresult, a refractive index Ny of the magnetic layer in a width directionand a refractive index Nz₂ of the magnetic layer in a thicknessdirection, measured by making an incidence ray incident in a widthdirection are obtained.

Fitting is performed by the following method.

Generally, “complex refractive index n=η+iκ”. Here, η is a real part ofa refractive index, κ is an extinction coefficient, and i is animaginary number. In a relation of complex permittivity ε=ε1+iε2 (ε1 andε2 satisfy a Kramers-Kronig relation), ε1=η²−κ², and ε2=2ηκ, in a caseof calculating Nx and Nz₁, complex permittivity of Nx isε_(x)=ε_(x)1+iε_(x)2 and complex permittivity of Nz₁ isε_(z1)=ε_(z1)1+iε_(z1)2.

ε_(x)2 is set as one Gaussian, any point with a peak position of 5.8 to5.1 eV and σ of 4 to 3.5 eV is set as a starting point, a parametercausing permittivity to be offset is provided outside a measurementwavelength range (400 to 700 nm), and least square fitting of themeasurement value is performed, to obtain Nx. Similarly, in ε_(z1)2, anypoint with a peak position of 3.2 to 2.9 eV and σ of 1.5 to 1.2 eV isset as a starting point, an offset parameter is provided, and leastsquare fitting of the measurement value is performed, to obtain Nz₁.Similarly, Ny and Nz₂ are also obtained. A refractive index Nxy of themagnetic layer, measured in an in-plane direction is obtained as“Nxy=(Nx+Ny)/2”. A refractive index Nz of the magnetic layer, measuredin a thickness direction is obtained as “Nz=(Nz₁+Nz₂)/2”. From theobtained Nxy and Nz, an absolute value ΔN of a difference therebetweenis obtained.

(3) Refractive Index Measurement of Non-Magnetic Layer

Similar to the above method except for the following points, refractiveindexes at a wavelength of 600 nm of the non-magnetic layer (arefractive index in a longitudinal direction, a refractive index in awidth direction, a refractive index in a thickness direction, measuredby making an incidence ray incident in a longitudinal direction, and arefractive index in a thickness direction, measured by making anincidence ray incident in a width direction) are obtained.

A wavelength of an incidence ray is changed by every 1.5 nm in a rangeof 250 to 700 nm.

A two-layer model of a non-magnetic layer and a non-magnetic support isused, here, the 0th layer, which is a substrate of the two-layer model,is the non-magnetic support, and the first layer is the non-magneticlayer. Considering only reflection at interfaces between air/anon-magnetic layer and a non-magnetic layer/a non-magnetic support, andassuming that there is no influence of back surface reflection of thenon-magnetic layer, the two-layer model is created.

In fitting, seven peaks (0.6 eV, 2.3 eV, 2.9 eV, 3.6 eV, 4.6 eV, 5.0 eV,6.0 eV) are assumed to be in an imaginary part (ε2) of the complexpermittivity and a parameter causing permittivity to be offset isprovided outside a measurement wavelength range (250 to 700 nm).

(4) Refractive Index Measurement of Non-Magnetic Support

Refractive indexes of the non-magnetic support at a wavelength of 600 nm(a refractive index in a longitudinal direction, a refractive index in awidth direction, a refractive index in a thickness direction, measuredby making an incidence ray incident in a longitudinal direction, and arefractive index in a thickness direction, measured by making anincidence ray incident in a width direction) used in order to obtain arefractive index of a non-magnetic layer by a two-layer model areobtained similar to the above method for measuring refractive indexes ofthe magnetic layer except for the following points.

Instead of using a two-layer model, a one-layer model for only surfacereflection is used.

Fitting is performed by a Cauchy model (n=A+B/λ², n is a refractiveindex, each of A and B is a constant determined by fitting, and λ is awavelength).

It is considered that in a case of reading data recorded on the magnetictape, the magnetic layer surface comes into contact with the readingelement and the magnetic layer surface is scraped, and thus scrapings(may be referred to as debris) are generated. The more these scrapingsare present between the magnetic layer surface and the reading element,the more unstable the contact state between the magnetic layer surfaceand the reading element becomes. The present inventors suppose that thiscauses a large change in a relative position (a relative positionalchange) between the reading element and the reading target track. Incontrast, ΔN obtained by the above method is considered to be a valuethat can serve as an index of a presence state of ferromagnetic powderin a surface layer region of the magnetic layer. The ΔN is supposed tobe a value affected by various factors such as a presence state of abinding agent and density distribution of ferromagnetic powder inaddition to an orientation state of ferromagnetic powder in the magneticlayer. It is considered that a magnetic layer in which ΔN is caused tobe 0.25 or more and 0.40 or less by controlling various factors has amagnetic layer surface with a high strength and is difficult to bescraped even though the magnetic layer contacts the reading element. Asa result, it is supposed that suppression of unstableness in a contactstate between the magnetic layer surface and the reading element due toscrapings generated by scraping the magnetic layer surface, contributesto suppression of occurrence of the above relative positional change.The present inventors consider that this aspect contributes to a moreappropriate waveform equalization process performed on each of thereading results obtained by a plurality of the reading elements, andleads to an increase in an acceptable amount of a deviation amount (atrack off-set amount), for ensuring excellent reproducing quality.

In addition, as described above, it is considered that formation of aservo pattern in a shape closer to a design shape also leads to anincrease in an acceptable amount of a deviation amount (a track off-setamount), for ensuring excellent reproducing quality. In this regard, thepresent inventors consider that the above difference (L_(99.9)−L_(0.1))is an index related to a shape of the servo pattern, and the difference(L_(99.9)−L_(0.1)) of 180 nm or less contributes to an increase in anacceptable amount of a deviation amount (a track off-set amount), forensuring excellent reproducing quality. Regarding a shape of a servopattern formed on the magnetic layer, as one of means for suppressingdeviation between a shape of a servo pattern (a magnetization region) tobe formed on the magnetic layer by applying a magnetic field by a servowrite head and a shape of a servo pattern actually formed on themagnetic layer, it is considered to increase a capacity of a servo writehead, specifically, to use a servo write head having a large magneticfield (leakage magnetic field). It is also considered that scrapings(debris) are generated in a case where a servo pattern is formed byapplying a magnetic field to the magnetic layer by the servo write headwhile contacting the magnetic layer surface. The more these scrapingsare present between the magnetic layer surface and the servo write head,the more unstable the contact state between the magnetic layer surfaceand the servo write head becomes. The present inventors suppose thatthis is a cause of deviation generated between a shape of the servopattern (a magnetization region) to be formed on the magnetic layer byapplying a magnetic field by the servo write head and a shape of a servopattern actually formed on the magnetic layer. On the other hand, thepresent inventors consider that the magnetic layer in which ΔN is 0.25or more and 0.40 or less and which is difficult to be scraped eventhough the magnetic layer contacts the servo write head contributes toformation of a servo pattern having a shape closer to a design shape,that is, the difference (L_(99.9)−L_(0.1)) of 180 nm or less.

Here, the above description is merely supposition and the presentinvention is not limited thereto.

Hereinafter, the magnetic tape will be described later in detail.

ΔN of Magnetic Layer

ΔN of a magnetic layer of the magnetic tape is 0.25 or more and 0.40 orless. From a viewpoint of more increasing an acceptable amount of adeviation amount (a track off-set amount), for ensuring excellentreproducing quality, ΔN is preferably 0.25 or more and 0.35 or less. Aspecific aspect of means for adjusting ΔN will be described later.

ΔN is an absolute value of a difference between Nxy and Nz. Nxy is arefractive index of the magnetic layer, measured in an in-planedirection, and Nz is a refractive index of the magnetic layer, measuredin a thickness direction. In an aspect, Nxy>Nz may be satisfied, and inanother aspect, Nxy<Nz may be satisfied. From a viewpoint ofelectromagnetic conversion characteristics of the magnetic tape, it ispreferable that Nxy>Nz, and therefore, a difference (Nxy−Nz) between Nxyand Nz is preferably 0.25 or more and 0.40 or less, and is morepreferably 0.25 or more and 0.35 or less. In an aspect, Nxy may be, forexample, in a range of 1.50 to 2.50. In an aspect, Nz may be, forexample, in a range of 1.30 to 2.50. Here, in the above-describedmagnetic tape, ΔN may be in a range of 0.25 or more and 0.40 or less,and Nxy and Nz are not limited to the above-exemplified ranges.

Various means for adjusting ΔN described above will be described later.

Difference (L_(99.9)−L_(0.1))

The difference (L_(99.9)−L_(0.1)) is 180 nm or less. It is supposed thatthis aspect also contributes to an increase in an acceptable amount of adeviation amount (a track off-set amount), for ensuring excellentreproducing quality. From the above viewpoint, the difference(L_(99.9)−L_(0.1)) is preferably 170 nm or less, more preferably 160 nmor less, and still more preferably 150 nm or less. Further, thedifference (L_(99.9)−L_(0.1)) may be, for example, 50 nm or more, 60 nmor more, 70 nm or more, 80 nm or more, 90 nm or more, or 100 nm or more.Here, it is considered that the smaller a value of the difference(L_(99.9)−L_(0.1)) is, the more preferable it is to increase theacceptable amount of a deviation amount (a track off-set amount), forensuring excellent reproducing quality, and thus the difference(L_(99.9)−L_(0.1)) may be below the lower limit exemplified above.

Next, a magnetic layer of the magnetic tape, and the like will befurther described.

Magnetic Layer

Ferromagnetic Powder

A magnetic layer includes ferromagnetic powder and a binding agent. Asthe ferromagnetic powder included in the magnetic layer, knownferromagnetic powder that is ferromagnetic powder used in the magneticlayer of various magnetic recording media, may be used. It is preferableto use ferromagnetic powder having a small average particle size, from aviewpoint of improvement of recording density. In this respect, anaverage particle size of the ferromagnetic powder is preferably 50 nm orless, more preferably 45 nm or less, still more preferably 40 nm orless, still more preferably 35 nm or less, still more preferably 30 nmor less, still more preferably 25 nm or less, and still more preferably20 nm or less. On the other hand, from a viewpoint of magnetizationstability, an average particle size of the ferromagnetic powder ispreferably 5 nm or more, more preferably 8 nm or more, still morepreferably 10 nm or more, and still more preferably 15 nm or more, andstill more preferably 20 nm or more.

Hexagonal Ferrite Powder

Preferable specific examples of ferromagnetic powder may includehexagonal ferrite powder. For details of the hexagonal ferrite powder,descriptions disclosed in paragraphs 0012 to 0030 of JP2011-225417A,paragraphs 0134 to 0136 of JP2011-216149A, paragraphs 0013 to 0030 ofJP2012-204726A, and paragraphs 0029 to 0084 of JP2015-127985A can bereferred to, for example.

In the present invention and this specification, “hexagonal ferritepowder” refers to ferromagnetic powder in which a hexagonal ferrite typecrystal structure is detected as a main phase by X-ray diffractionanalysis. The main phase refers to a structure to which the highestintensity diffraction peak in an X-ray diffraction spectrum obtained byX-ray diffraction analysis is attributed. For example, in a case wherethe highest intensity diffraction peak is attributed to a hexagonalferrite crystal structure in an X-ray diffraction spectrum obtained byX-ray diffraction analysis, it is determined that the hexagonal ferritecrystal structure is detected as the main phase. In a case where only asingle structure is detected by X-ray diffraction analysis, thisdetected structure is taken as the main phase. The hexagonal ferritetype crystal structure includes at least an iron atom, a divalent metalatom and an oxygen atom, as a constituent atom. The divalent metal atomis a metal atom that can be a divalent cation as an ion, and examplesthereof may include an alkaline earth metal atom such as a strontiumatom, a barium atom, and a calcium atom, a lead atom, and the like. Inthe present invention and this specification, hexagonal strontiumferrite powder means that a main divalent metal atom contained in thepowder is a strontium atom, and hexagonal barium ferrite powder meansthat a main divalent metal atom included in the powder is a barium atom.The main divalent metal atom refers to a divalent metal atom thataccounts for the most on an at % basis among divalent metal atomsincluded in the powder. Here, a rare earth atom is not included in theabove divalent metal atom. The “rare earth atom” in the presentinvention and this specification is selected from the group consistingof a scandium atom (Sc), an yttrium atom (Y), and a lanthanoid atom. TheLanthanoid atom is selected from the group consisting of a lanthanumatom (La), a cerium atom (Ce), a praseodymium atom (Pr), a neodymiumatom (Nd), a promethium atom (Pm), a samarium atom (Sm), a europium atom(Eu), a gadolinium atom (Gd), a terbium atom (Tb), a dysprosium atom(Dy), a holmium atom (Ho), an erbium atom (Er), a thulium atom (Tm), anytterbium atom (Yb), and a lutetium atom (Lu).

Hereinafter, the hexagonal strontium ferrite powder which is an aspectof the hexagonal ferrite powder will be described in more detail.

An activation volume of the hexagonal strontium ferrite powder ispreferably in a range of 800 to 1600 nm³. The particulate hexagonalstrontium ferrite powder exhibiting an activation volume in the aboverange is suitable for manufacturing a magnetic tape exhibiting excellentelectromagnetic conversion characteristics. An activation volume of thehexagonal strontium ferrite powder is preferably 800 nm³ or more, andmay be, for example, 850 nm³ or more. Further, from a viewpoint offurther improving electromagnetic conversion characteristics, anactivation volume of the hexagonal strontium ferrite powder is morepreferably 1500 nm³ or less, still more preferably 1400 nm³ or less,still more preferably 1300 nm³ or less, still more preferably 1200 nm³or less, and still more preferably 1100 nm³ or less. The same applies toan activation volume of the hexagonal barium ferrite powder.

The “activation volume” is a unit of magnetization reversal and is anindex indicating a magnetic size of a particle. An activation volumedescribed in the present invention and this specification and ananisotropy constant Ku which will be described later are values obtainedfrom the following relational expression between a coercivity Hc and anactivation volume V, by performing measurement in an Hc measurementportion at a magnetic field sweep rate of 3 minutes and 30 minutes usinga vibrating sample magnetometer (measurement temperature: 23° C.±1° C.).In a unit of the anisotropy constant Ku, 1 erg/cc=1.0×10⁻¹ J/m³.Hc=2Ku/Ms{1−[(kT/KuV)ln(At/0.693)]^(1/2)}

[In the above formula, Ku: anisotropy constant (unit: J/m³), Ms:saturation magnetization (Unit: kA/m), k: Boltzmann constant, T:absolute temperature (unit: K), V: activation volume (unit: cm³), A:spin precession frequency (unit: s⁻¹), t: magnetic field reversal time(unit: s)]

An index for reducing thermal fluctuation, in other words, improvingthermal stability may include an anisotropy constant Ku. The hexagonalstrontium ferrite powder may preferably have Ku of 1.8×10⁵ J/m³ or more,and more preferably have a Ku of 2.0×10⁵ J/m³ or more. Ku of thehexagonal strontium ferrite powder may be, for example, 2.5×10⁵ J/m³ orless. Here, it means that the higher Ku is, the higher thermal stabilityis, this is preferable, and thus, a value thereof is not limited to thevalues exemplified above.

The hexagonal strontium ferrite powder may or may not include a rareearth atom. In a case where the hexagonal strontium ferrite powderincludes a rare earth atom, it is preferable to include a rare earthatom at a content (bulk content) of 0.5 to 5.0 at % with respect to 100at % of an iron atom. In an aspect, the hexagonal strontium ferritepowder including a rare earth atom may have a rare earth atom surfacelayer portion uneven distribution property. In the present invention andthis specification, the “rare earth atom surface layer portion unevendistribution property” means that a rare earth atom content with respectto 100 at % of an iron atom in a solution obtained by partiallydissolving hexagonal strontium ferrite powder with an acid (hereinafter,referred to as a “rare earth atom surface layer portion content” orsimply a “surface layer portion content” for a rare earth atom) and arare earth atom content with respect to 100 at % of an iron atom in asolution obtained by totally dissolving hexagonal strontium ferritepowder with an acid (hereinafter, referred to as a “rare earth atom bulkcontent” or simply a “bulk content” for a rare earth atom) satisfy aratio of a rare earth atom surface layer portion content/a rare earthatom bulk content >1.0. A rare earth atom content in hexagonal ferritepowder which will be described later is the same meaning as the rareearth atom bulk content. On the other hand, partial dissolution using anacid dissolves a surface layer portion of a particle configuringhexagonal strontium ferrite powder, and thus, a rare earth atom contentin a solution obtained by partial dissolution is a rare earth atomcontent in a surface layer portion of a particle configuring hexagonalstrontium ferrite powder. A rare earth atom surface layer portioncontent satisfying a ratio of “rare earth atom surface layer portioncontent/rare earth atom bulk content>1.0” means that in a particle ofhexagonal strontium ferrite powder, rare earth atoms are unevenlydistributed in a surface layer portion (that is, more than an inside).The surface layer portion in the present invention and thisspecification means a partial region from a surface of a particleconfiguring hexagonal strontium ferrite powder toward an inside.

In a case where hexagonal ferrite powder includes a rare earth atom, arare earth atom content (bulk content) is preferably in a range of 0.5to 5.0 at % with respect to 100 at % of an iron atom. It is consideredthat a bulk content in the above range of the included rare earth atomand uneven distribution of the rare earth atoms in a surface layerportion of a particle configuring hexagonal strontium ferrite powdercontribute to suppression of a decrease in a reproducing output inrepeated reproduction. It is supposed that this is because hexagonalstrontium ferrite powder includes a rare earth atom with a bulk contentin the above range, and rare earth atoms are unevenly distributed in asurface layer portion of a particle configuring hexagonal strontiumferrite powder, and thus it is possible to increase an anisotropyconstant Ku. The higher a value of an anisotropy constant Ku is, themore a phenomenon called so-called thermal fluctuation can be suppressed(in other words, thermal stability can be improved). By suppressingoccurrence of thermal fluctuation, it is possible to suppress a decreasein reproducing output during repeated reproduction. It is supposed thatuneven distribution of rare earth atoms in a particulate surface layerportion of hexagonal strontium ferrite powder contributes tostabilization of spins of iron (Fe) sites in a crystal lattice of asurface layer portion, and thus, an anisotropy constant Ku may beincreased.

Moreover, it is supposed that the use of hexagonal strontium ferritepowder having a rare earth atom surface layer portion unevendistribution property as a ferromagnetic powder in the magnetic layeralso contributes to inhibition of a surface of the magnetic layer frombeing scraped by being slid with respect to the magnetic head. That is,it is supposed that hexagonal strontium ferrite powder having rare earthatom surface layer portion uneven distribution property can alsocontribute to an improvement of running durability of the magnetic tape.It is supposed that this may be because uneven distribution of rareearth atoms on a surface of a particle configuring hexagonal strontiumferrite powder contributes to an improvement of interaction between theparticle surface and an organic substance (for example, a binding agentand/or an additive) included in the magnetic layer, and, as a result, astrength of the magnetic layer is improved.

From a viewpoint of further suppressing a decrease in reproducing outputduring repeated reproduction and/or a viewpoint of further improving therunning durability, the rare earth atom content (bulk content) is morepreferably in a range of 0.5 to 4.5 at %, still more preferably in arange of 1.0 to 4.5 at %, and still more preferably in a range of 1.5 to4.5 at %. The bulk content is a content obtained by totally dissolvinghexagonal strontium ferrite powder. In the present invention and thisspecification, unless otherwise noted, the content of an atom means abulk content obtained by totally dissolving hexagonal strontium ferritepowder. The hexagonal strontium ferrite powder including a rare earthatom may include only one kind of rare earth atom as the rare earthatom, or may include two or more kinds of rare earth atoms. The bulkcontent in the case of including two or more types of rare earth atomsis obtained for the total of two or more types of rare earth atoms. Thisalso applies to other components in the present invention and thisspecification. That is, unless otherwise noted, a certain component maybe used alone or in combination of two or more. A content amount orcontent in a case where two or more components are used refers to thatfor the total of two or more components.

In a case where the hexagonal strontium ferrite powder includes a rareearth atom, the included rare earth atom may be any one or more of rareearth atoms. As a rare earth atom that is preferable from a viewpoint offurther suppressing a decrease in reproducing output in repeatedreproduction, there are a neodymium atom, a samarium atom, an yttriumatom, and a dysprosium atom, here, a neodymium atom, a samarium atom,and an yttrium atom are more preferable, and a neodymium atom is stillmore preferable.

In the hexagonal strontium ferrite powder having a rare earth atomsurface layer portion uneven distribution property, the rare earth atomsmay be unevenly distributed in the surface layer portion of a particleconfiguring the hexagonal strontium ferrite powder, and the degree ofuneven distribution is not limited. For example, for a hexagonalstrontium ferrite powder having a rare earth atom surface layer portionuneven distribution property, a ratio between a surface layer portioncontent of a rare earth atom obtained by partial dissolution underdissolution conditions which will be described later and a bulk contentof a rare earth atom obtained by total dissolution under dissolutionconditions which will be described later, that is, “surface layerportion content/bulk content” exceeds 1.0 and may be 1.5 or more. A“surface layer portion content/bulk content” larger than 1.0 means thatin a particle configuring the hexagonal strontium ferrite powder, rareearth atoms are unevenly distributed in the surface layer (that is, morethan the inside). Further, a ratio between a surface layer portioncontent of a rare earth atom obtained by partial dissolution underdissolution conditions which will be described later and a bulk contentof a rare earth atom obtained by total dissolution under the dissolutionconditions which will be described later, that is, “surface layerportion content/bulk content” may be, for example, 10.0 or less, 9.0 orless, 8.0 or less, 7.0 or less, 6.0 or less, 5.0 or less, or 4.0 orless. Here, in the hexagonal strontium ferrite powder having a rareearth atom surface layer portion uneven distribution property, the rareearth atoms may be unevenly distributed in the surface layer portion ofa particle configuring the hexagonal strontium ferrite powder, and the“surface layer portion content/bulk content” is not limited to theillustrated upper limit or lower limit.

The partial dissolution and the total dissolution of the hexagonalstrontium ferrite powder will be described below. For the hexagonalstrontium ferrite powder that exists as a powder, the partially andtotally dissolved sample powder is taken from the same lot of powder. Onthe other hand, for the hexagonal strontium ferrite powder included inthe magnetic layer of the magnetic tape, a part of the hexagonalstrontium ferrite powder taken out from the magnetic layer is subjectedto partial dissolution, and the other part is subjected to totaldissolution. The hexagonal strontium ferrite powder can be taken outfrom the magnetic layer by a method described in paragraph 0032 ofJP2015-091747A, for example.

The partial dissolution means that dissolution is performed such that,at the end of dissolution, the residue of the hexagonal strontiumferrite powder can be visually checked in the solution. For example, bypartial dissolution, it is possible to dissolve a region of 10 to 20mass % of the particle configuring the hexagonal strontium ferritepowder with the total particle being 100 mass %. On the other hand, thetotal dissolution means that dissolution is performed such that, at theend of dissolution, the residue of the hexagonal strontium ferritepowder can not be visually checked in the solution.

The partial dissolution and measurement of the surface layer portioncontent are performed by the following method, for example. Here, thefollowing dissolution conditions such as an amount of sample powder areillustrative, and dissolution conditions for partial dissolution andtotal dissolution can be employed in any manner.

A container (for example, a beaker) containing 12 mg of sample powderand 10 ml of 1 mol/L hydrochloric acid is held on a hot plate at a settemperature of 70° C. for 1 hour. The obtained solution is filtered by amembrane filter of 0.1 μm. Elemental analysis of the filtrated solutionis performed by an inductively coupled plasma (ICP) analyzer. In thisway, the surface layer portion content of a rare earth atom with respectto 100 at % of an iron atom can be obtained. In a case where a pluralityof types of rare earth atoms are detected by elemental analysis, thetotal content of all rare earth atoms is defined as the surface layerportion content. This also applies to the measurement of the bulkcontent.

On the other hand, the total dissolution and measurement of the bulkcontent are performed by the following method, for example.

A container (for example, a beaker) containing 12 mg of sample powderand 10 ml of 4 mol/L hydrochloric acid is held on a hot plate at a settemperature of 80° C. for 3 hours. Thereafter, the method is carried outin the same manner as the partial dissolution and the measurement of thesurface layer portion content, and the bulk content with respect to 100at % of an iron atom can be obtained.

From a viewpoint of increasing the reproducing output in a case ofreproducing information recorded on the magnetic tape, it is desirablethat mass magnetization σs of the ferromagnetic powder included in themagnetic tape is high. In this regard, the hexagonal strontium ferritepowder including a rare earth atom but not having the rare earth atomsurface layer portion uneven distribution property tends to have σslargely lower than the hexagonal strontium ferrite powder including norare earth atom. On the other hand, it is considered that hexagonalstrontium ferrite powder having a rare earth atom surface layer portionuneven distribution property is preferable in suppressing such a largedecrease in σs. In an aspect, σs of the hexagonal strontium ferritepowder may be 45 A·m²/kg or more, and may be 47 A·m²/kg or more. On theother hand, from a viewpoint of noise reduction, σs is preferably 80A·m²/kg or less and more preferably 60 A·m²/kg or less. σs can bemeasured using a known measuring device, such as a vibrating samplemagnetometer, capable of measuring magnetic properties. In the presentinvention and this specification, unless otherwise noted, the massmagnetization σs is a value measured at a magnetic field intensity of1194 kA/m (15 kOe).

Regarding the content (bulk content) of a constituent atom of thehexagonal ferrite powder, the strontium atom content may be, forexample, in a range of 2.0 to 15.0 at % with respect to 100 at % of aniron atom. In an aspect, in the hexagonal strontium ferrite powder, adivalent metal atom included in the powder may be only a strontium atom.In another aspect, the hexagonal strontium ferrite powder may includeone or more other divalent metal atoms in addition to a strontium atom.For example, a barium atom and/or a calcium atom may be included. In acase where another divalent metal atom other than a strontium atom isincluded, a barium atom content and a calcium atom content in thehexagonal strontium ferrite powder are, for example, in a range of 0.05to 5.0 at % with respect to 100 at % of an iron atom, respectively.

As a crystal structure of hexagonal ferrite, a magnetoplumbite type(also called an “M type”), a W type, a Y type, and a Z type are known.The hexagonal strontium ferrite powder may have any crystal structure.The crystal structure can be checked by X-ray diffraction analysis. Inthe hexagonal strontium ferrite powder, a single crystal structure ortwo or more crystal structures may be detected by X-ray diffractionanalysis. For example, according to an aspect, in the hexagonalstrontium ferrite powder, only the M-type crystal structure may bedetected by X-ray diffraction analysis. For example, M-type hexagonalferrite is represented by a composition formula of AFe₁₂O₁₉. Here, Arepresents a divalent metal atom, and in a case where the hexagonalstrontium ferrite powder is the M-type, A is only a strontium atom (Sr),or in a case where, as A, a plurality of divalent metal atoms areincluded, as described above, a strontium atom (Sr) accounts for themost on an at % basis. The divalent metal atom content of the hexagonalstrontium ferrite powder is usually determined by the type of crystalstructure of the hexagonal ferrite and is not particularly limited. Thesame applies to the iron atom content and the oxygen atom content. Thehexagonal strontium ferrite powder may include at least an iron atom, astrontium atom, and an oxygen atom, and may further include a rare earthatom. Furthermore, the hexagonal strontium ferrite powder may or may notinclude atoms other than these atoms. As an example, the hexagonalstrontium ferrite powder may include an aluminum atom (A1). A content ofan aluminum atom can be, for example, 0.5 to 10.0 at % with respect to100 at % of an iron atom. From a viewpoint of further suppressing adecrease in reproducing output in repeated reproduction, the hexagonalstrontium ferrite powder includes an iron atom, a strontium atom, anoxygen atom, and a rare earth atom, and the content of atoms other thanthese atoms is preferably 10.0 at % or less, more preferably in a rangeof 0 to 5.0 at %, and may be 0 at % with respect to 100 at % of an ironatom. That is, in an aspect, the hexagonal strontium ferrite powder maynot include atoms other than an iron atom, a strontium atom, an oxygenatom, and a rare earth atom. The content expressed in at % is obtainedby converting a content of each atom (unit: mass %) obtained by totallydissolving hexagonal strontium ferrite powder into a value expressed inat % using an atomic weight of each atom. Further, in the presentinvention and this specification, “not include” for a certain atom meansthat a content measured by an ICP analyzer after total dissolution is 0mass %. A detection limit of the ICP analyzer is usually 0.01 ppm (partper million) or less on a mass basis. The “not included” is used as ameaning including that an atom is included in an amount less than thedetection limit of the ICP analyzer. In an aspect, the hexagonalstrontium ferrite powder may not include a bismuth atom (Bi).

Metal Powder

As a preferred specific example of the ferromagnetic powder,ferromagnetic metal powder can also be used. For details of theferromagnetic metal powder, descriptions disclosed in paragraphs 0137 to0141 of JP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351A canbe referred to, for example.

ε-Iron Oxide Powder

As a preferred specific example of the ferromagnetic powder, ε-ironoxide powder can also be used. In the present invention and thisspecification, “ε-iron oxide powder” refers to ferromagnetic powder inwhich a ε-iron oxide type crystal structure is detected as a main phaseby X-ray diffraction analysis. For example, in a case where the highestintensity diffraction peak is attributed to a ε-iron oxide type crystalstructure in an X-ray diffraction spectrum obtained by X-ray diffractionanalysis, it is determined that the ε-iron oxide type crystal structureis detected as the main phase. As a manufacturing method of ε-iron oxidepowder, a manufacturing method from a goethite, a reverse micellemethod, and the like are known. All of the manufacturing methods arewell known. Regarding a method of manufacturing ε-iron oxide powder inwhich a part of Fe is substituted with substitutional atoms such as Ga,Co, Ti, Al, or Rh, a description disclosed in J. Jpn. Soc. PowderMetallurgy Vol. 61 Supplement, No. 51, pp. S280-S284, J. Mater. Chem. C,2013, 1, pp. 5200-5206 can be referred to, for example. Here, themanufacturing method of ε-iron oxide powder capable of being used as theferromagnetic powder in the magnetic layer of the magnetic tape is notlimited to the methods described here.

An activation volume of the ε-iron oxide powder is preferably in a rangeof 300 to 1500 nm³. The particulate ε-iron oxide powder exhibiting anactivation volume in the above range is suitable for manufacturing amagnetic tape exhibiting excellent electromagnetic conversioncharacteristics. An activation volume of the ε-iron oxide powder ispreferably 300 nm³ or more, and may be, for example, 500 nm³ or more.Further, from a viewpoint of further improving electromagneticconversion characteristics, an activation volume of the ε-iron oxidepowder is more preferably 1400 nm³ or less, still more preferably 1300nm³ or less, still more preferably 1200 nm³ or less, and still morepreferably 1100 nm³ or less.

An index for reducing thermal fluctuation, in other words, improvingthermal stability may include an anisotropy constant Ku. The ε-ironoxide powder preferably has Ku of 3.0×10⁴ J/m³ or more, and morepreferably has Ku of 8.0×10⁴ J/m³ or more. Ku of the ε-iron oxide powdermay be, for example, 3.0×10⁵ J/m³ or less. Here, it means that thehigher Ku is, higher thermal stability is, this is preferable, and thus,a value thereof is not limited to the values exemplified above.

From a viewpoint of increasing the reproducing output in a case ofreproducing information recorded on the magnetic tape, it is desirablethat mass magnetization σs of the ferromagnetic powder included in themagnetic tape is high. In this regard, in an aspect, σs of the ε-ironoxide powder may be 8 A·m²/kg or more, and may be 12 A·m²/kg or more. Onthe other hand, from a viewpoint of noise reduction, σs of the ε-ironoxide powder is preferably 40 A·m²/kg or less and more preferably 35A·m²/kg or less.

In the present invention and this specification, unless otherwise noted,an average particle size of various powders such as the ferromagneticpowder is a value measured by the following method using a transmissionelectron microscope.

The powder is imaged at a magnification ratio of 100,000 with atransmission electron microscope, and the image is printed on printingpaper so that the total magnification ratio becomes 500,000 to obtain animage of particles configuring the powder. A target particle is selectedfrom the obtained image of particles, an outline of the particle istraced with a digitizer, and a size of the particle (primary particle)is measured. The primary particle is an independent particle which isnot aggregated.

The measurement described above is performed regarding 500 particlesrandomly extracted. An arithmetic average of the particle sizes of 500particles obtained as described above is an average particle size of thepowder. As the transmission electron microscope, a transmission electronmicroscope H-9000 manufactured by Hitachi, Ltd. can be used, forexample. In addition, the measurement of the particle size can beperformed by well-known image analysis software, for example, imageanalysis software KS-400 manufactured by Carl Zeiss. The averageparticle size shown in examples which will be described later is a valuemeasured by using a transmission electron microscope H-9000 manufacturedby Hitachi, Ltd. as the transmission electron microscope, and imageanalysis software KS-400 manufactured by Carl Zeiss as the imageanalysis software, unless otherwise noted. In the present invention andthis specification, the powder means an aggregate of a plurality ofparticles. For example, ferromagnetic powder means an aggregate of aplurality of ferromagnetic particles. Further, the aggregate of theplurality of particles not only includes an aspect in which particlesconfiguring the aggregate directly come into contact with each other,but also includes an aspect in which a binding agent or an additivewhich will be described later is interposed between the particles. Theterm “particle” is used to describe a powder in some cases.

As a method of taking sample powder from the magnetic tape in order tomeasure the particle size, a method disclosed in a paragraph of 0015 ofJP2011-048878A can be used, for example.

In the present invention and this specification, unless otherwise noted,

(1) in a case where the shape of the particle observed in the particleimage described above is a needle shape, a fusiform shape, or a columnarshape (here, a height is greater than a maximum long diameter of abottom surface), the size (particle size) of the particles configuringthe powder is shown as a length of a long axis configuring the particle,that is, a long axis length,

(2) in a case where the shape of the particle is a plate shape or acolumnar shape (here, a thickness or a height is smaller than a maximumlong diameter of a plate surface or a bottom surface), the particle sizeis shown as a maximum long diameter of the plate surface or the bottomsurface, and

(3) in a case where the shape of the particle is a sphere shape, apolyhedron shape, or an unspecified shape, and the long axis configuringthe particles cannot be specified from the shape, the particle size isshown as an equivalent circle diameter. The equivalent circle diameteris a value obtained by a circle projection method.

In addition, regarding an average acicular ratio of the powder, a lengthof a short axis, that is, a short axis length of each of the particlesis measured in the measurement described above, a value of (long axislength/short axis length) of each particle is obtained, and anarithmetic average of the values obtained regarding 500 particles iscalculated. Here, unless otherwise noted, in a case of (1), the shortaxis length as the definition of the particle size is a length of ashort axis configuring the particle, in a case of (2), the short axislength is a thickness or a height, and in a case of (3), the long axisand the short axis are not distinguished, thus, the value of (long axislength/short axis length) is assumed as 1, for convenience.

In addition, unless otherwise noted, in a case where the shape of theparticle is specified, for example, in a case of definition of theparticle size (1), the average particle size is an average long axislength, and in a case of the definition (2), the average particle sizeis an average plate diameter. In a case of the definition (3), theaverage particle size is an average diameter (also referred to as anaverage particle diameter).

In an aspect, the shape of the ferromagnetic particle configuring theferromagnetic powder included in the magnetic layer may be a plateshape. Hereinafter, the ferromagnetic powder configured withferromagnetic particles of the plate shape is referred to asplate-shaped ferromagnetic powder. An average plate shape ratio of theplate-shaped ferromagnetic powder is preferably in a range of 2.5 to5.0. The average plate shape ratio is an arithmetic average of (maximummajor axis/thickness or height) in the case of the above definition (2).As the average plate shape ratio increases, an orientation process tendsto increase uniformity of the orientation state of the ferromagneticparticles configuring the plate-shaped ferromagnetic powder, and thevalue of ΔN tends to increase.

A content (filling percentage) of the ferromagnetic powder of themagnetic layer is preferably 50 to 90 mass % and more preferably 60 to90 mass %. A component other than the ferromagnetic powder of themagnetic layer is at least a binding agent, and one or more kinds ofadditives can be randomly included. A high filling percentage of theferromagnetic powder in the magnetic layer is preferable from aviewpoint of improvement of recording density.

Binding Agent and Curing Agent

The magnetic tape is a coating type magnetic tape and includes a bindingagent in the magnetic layer. The binding agent is one or more kinds ofresins. The resin may be a homopolymer or a copolymer. As the bindingagent included in the magnetic layer, a resin selected from apolyurethane resin, a polyester resin, a polyamide resin, a vinylchloride resin, an acrylic resin obtained by copolymerizing styrene,acrylonitrile, methyl methacrylate, or the like, a cellulose resin suchas nitrocellulose, an epoxy resin, a phenoxy resin, and apolyvinylalkylal resin such as polyvinyl acetal or polyvinyl butyral canbe used alone or a plurality of the resins can be mixed with each otherto be used. Among these, a polyurethane resin, an acrylic resin, acellulose resin, and a vinyl chloride resin are preferable. These resinscan be used as the binding agent even in the non-magnetic layer and/or aback coating layer which will be described later. For the binding agentdescribed above, description disclosed in paragraphs 0029 to 0031 ofJP2010-024113A can be referred to. In addition, the binding agent may bea radiation curable resin such as an electron beam-curable resin. Forthe radiation curable resin, descriptions disclosed in paragraphs 0044and 0045 of JP2011-048878A can be referred to.

An average molecular weight of the resin used as the binding agent canbe, for example, 10,000 or more and 200,000 or less as a weight-averagemolecular weight. The weight-average molecular weight of the presentinvention and this specification is a value obtained by performingpolystyrene conversion of a value measured by gel permeationchromatography (GPC). As the measurement conditions, the followingconditions can be used. The weight-average molecular weight shown inexamples which will be described later is a value obtained by performingpolystyrene conversion of a value measured under the followingmeasurement conditions.

GPC device: HLC-8120 (manufactured by Tosoh Corporation)

Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8mm ID (inner diameter)×30.0 cm)

Eluent: Tetrahydrofuran (THF)

In an aspect, as a binding agent, a binding agent containing an acidicgroup can be used. The acidic group in the present invention and thisspecification is used in a meaning including a form of a group capableof releasing H⁺ in water or a solvent including water (aqueous solvent)to be dissociated into an anion and a salt thereof. As a specificexample of an acidic group, a form of each of a sulfonic acid group, asulfuric acid group, a carboxy group, a phosphoric acid group, and asalt thereof, can be used, for example. For example, a form of a salt ofa sulfonic acid group (—SO₃H) means a group represented by —SO₃M, whereM represents a group representing an atom (for example, an alkali metalatom or the like) which can be a cation in water or an aqueous solvent.The same applies to the form of each of salts of the various groupsdescribed above. As an example of a binding agent containing an acidicgroup, a resin containing at least one type of acidic group selectedfrom the group consisting of a sulfonic acid group and a salt thereof(for example, a polyurethane resin, a vinyl chloride resin, or the like)can be used, for example. Here, the resin included in the magnetic layeris not limited to these resins. In the binding agent containing anacidic group, an acidic group content may be, for example, in a range of20 to 500 eq/ton. Contents of various functional groups such as anacidic group included in a resin, can be obtained by a well-known methodaccording to the kind of functional group. As the binding agent having ahigher acidic group content is used, the value of ΔN tends to increase.The binding agent can be used in a magnetic layer forming composition inan amount of, for example, 1.0 to 30.0 parts by mass, and preferably 1.0to 20.0 parts by mass with respect to 100.0 parts by mass of theferromagnetic powder. The value of ΔN tends to increase as the amount ofbinding agent used for the ferromagnetic powder increases.

In addition, a curing agent can also be used together with a resinusable as the binding agent. As the curing agent, in an aspect, athermosetting compound which is a compound in which a curing reaction(crosslinking reaction) proceeds due to heating can be used, and inanother aspect, a photocurable compound in which a curing reaction(crosslinking reaction) proceeds due to light irradiation can be used.At least a part of the curing agent is included in the magnetic layer ina state of being reacted (crosslinked) with other components such as thebinding agent, by proceeding the curing reaction in a magnetic layerforming step. The same applies to the layer formed using thiscomposition in a case where the composition used to form the other layerincludes a curing agent. The preferred curing agent is a thermosettingcompound, and polyisocyanate is suitable for this. For details of thepolyisocyanate, descriptions disclosed in paragraphs 0124 and 0125 ofJP2011-216149A can be referred to. The curing agent can be used in themagnetic layer forming composition in an amount of, for example, 0 to80.0 parts by mass, and preferably 50.0 to 80.0 parts by mass, from aviewpoint of improvement of a strength of the magnetic layer, withrespect to 100.0 parts by mass of the binding agent.

Additive

The magnetic layer may include a ferromagnetic powder and a bindingagent, and, as necessary, include one or more kinds of additives. As theadditive, the curing agent described above is used as an example. Inaddition, examples of the additive which can be included in the magneticlayer include non-magnetic powder (for example, inorganic powder orcarbon black), a lubricant, a dispersing agent, a dispersing assistant,an antibacterial agent, an antistatic agent, and an antioxidant. As thenon-magnetic powder, non-magnetic powder which can function as anabrasive, or non-magnetic powder which can function as a projectionformation agent which forms projections suitably protruded from thesurface of the magnetic layer (for example, non-magnetic colloidalparticles) is used. An average particle size of the colloidal silica(silica colloidal particles) shown in examples which will be describedlater is a value obtained by a method disclosed in a paragraph 0015 ofJP2011-048878A as a measurement method of an average particle diameter.As the additive, a commercially available product can be suitablyselected or manufactured by a well-known method according to the desiredproperties, and any amount thereof can be used. As an example of theadditive which can be used in the magnetic layer including the abrasive,a dispersing agent disclosed in paragraphs 0012 to 0022 ofJP2013-131285A can be used as a dispersing agent for improvingdispersibility of the abrasive. For example, for the lubricant,descriptions disclosed in paragraphs 0030 to 0033, 0035, and 0036 ofJP2016-126817A can be referred to. The non-magnetic layer may include alubricant. For the lubricant which may be included in the non-magneticlayer, descriptions disclosed in paragraphs 0030, 0031, 0034, 0035, and0036 of JP2016-126817A can be referred to. For the dispersing agent,descriptions disclosed in paragraphs 0061 and 0071 of JP2012-133837A canbe referred to. The dispersing agent may be included in the non-magneticlayer. For the dispersing agent which can be included in thenon-magnetic layer, a description disclosed in a paragraph 0061 ofJP2012-133837A can be referred to.

The magnetic layer described above can be provided on the surface of thenon-magnetic support directly or indirectly through the non-magneticlayer.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tape mayinclude a magnetic layer on a non-magnetic support directly, or mayinclude a non-magnetic layer including non-magnetic powder and a bindingagent between the non-magnetic support and the magnetic layer. Thenon-magnetic powder used in the non-magnetic layer may be powder ofinorganic substance or powder of organic substance. In addition, carbonblack and the like can be used. Examples of the inorganic substanceinclude metal, metal oxide, metal carbonate, metal sulfate, metalnitride, metal carbide, and metal sulfide. These non-magnetic powderscan be purchased as a commercially available product or can bemanufactured by a well-known method. For details thereof, descriptionsdisclosed in paragraphs 0146 to 0150 of JP2011-216149A can be referredto. For carbon black which can be used in the non-magnetic layer,descriptions disclosed in paragraphs 0040 and 0041 of JP2010-024113A canbe referred to. The content (filling percentage) of the non-magneticpowder of the non-magnetic layer is preferably 50 to 90 mass % and morepreferably 60 to 90 mass %.

In regards to other details of a binding agent or an additive of thenon-magnetic layer, the well-known technology regarding the non-magneticlayer can be applied. In addition, in regards to the type and thecontent of the binding agent, and the type and the content of theadditive, for example, the well-known technology regarding the magneticlayer can be applied.

The non-magnetic layer of the magnetic tape also includes asubstantially non-magnetic layer including a small amount offerromagnetic powder as impurities, for example, or intentionally,together with the non-magnetic powder. Here, the substantiallynon-magnetic layer is a layer having a residual magnetic flux densityequal to or smaller than 10 mT, a layer having a coercivity equal to orsmaller than 7.96 kA/m (100 Oe), or a layer having a residual magneticflux density equal to or smaller than 10 mT and a coercivity equal to orsmaller than 7.96 kA/m (100 Oe). It is preferable that the non-magneticlayer does not have a residual magnetic flux density and a coercivity.

Non-Magnetic Support

Next, the non-magnetic support will be described. As the non-magneticsupport (hereinafter, also simply referred to as a “support”),well-known components such as polyethylene terephthalate, polyethylenenaphthalate, polyamide, polyamide imide, and aromatic polyamidesubjected to biaxial stretching are used. Among these, polyethyleneterephthalate, polyethylene naphthalate, and polyamide are preferable.Corona discharge, plasma treatment, easy-bonding treatment, or thermaltreatment may be performed with respect to these supports in advance.

Back Coating Layer

The magnetic tape may or may not include a back coating layer includingnon-magnetic powder and a binding agent on a surface side of thenon-magnetic support opposite to the surface provided with the magneticlayer. Preferably, the back coating layer includes one or both of carbonblack and inorganic powder. In regards to the binding agent included inthe back coating layer and various additives which can be randomlyincluded in the back coating layer, the well-known technology regardingthe back coating layer can be applied, and the well-known technologyregarding the treatment of the magnetic layer and/or the non-magneticlayer can be applied. For example, for the back coating layer,descriptions disclosed in paragraphs 0018 to 0020 of JP2006-331625A andpage 4, line 65, to page 5, line 38, of U.S. Pat. No. 7,029,774B can bereferred to.

Various Thicknesses

A thickness of the non-magnetic support is, for example, 3.0 to 80.0 μm,preferably 3.0 to 50.0 μm, and more preferably 3.0 to 10.0 μm.

A thickness of the magnetic layer can be optimized according tosaturation magnetization of the used magnetic head, a head gap length, aband of a recording signal, and the like. A thickness of the magneticlayer is generally 10 nm to 100 nm, and preferably 20 to 90 nm and morepreferably 30 to 70 nm from a viewpoint of high density recording. Themagnetic layer may be at least a single layer, the magnetic layer may beseparated into two or more layers having different magnetic properties,and a configuration of a well-known multilayered magnetic layer can beapplied as the magnetic layer. A thickness of the magnetic layer in acase where the magnetic layer is separated into two or more layers is atotal thickness of the layers.

A thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm andis preferably 0.1 to 1.0 μm.

A thickness of the back coating layer is preferably equal to or smallerthan 0.9 μm and more preferably 0.1 to 0.7 μm.

Thicknesses of each layer and the non-magnetic support are obtained byexposing a cross section of the magnetic tape in a thickness directionby known means such as an ion beam or a microtome, and then performing across section observation using a scanning transmission electronmicroscope (STEM). For specific examples of a method of measuring athickness, descriptions relating to a method of measuring a thickness inexamples which will be described later can be referred to.

Method of Manufacturing Magnetic Tape

Manufacturing of Magnetic Tape Having Servo Pattern

Preparation of Each Layer Forming Composition

A step of preparing a composition for forming the magnetic layer, thenon-magnetic layer, or the back coating layer generally includes atleast a kneading step, a dispersing step, and a mixing step providedbefore and after these steps, as necessary. Each step may be dividedinto two or more stages. The component used in the preparation of eachlayer forming composition may be added at an initial stage or in amiddle stage of each step. As a solvent, one kind or two or more kindsof various solvents generally used for manufacturing a coating typemagnetic recording medium can be used. For the solvent, a descriptiondisclosed in a paragraph 0153 of JP2011-216149A can be referred to, forexample. In addition, each component may be separately added in two ormore steps. For example, a binding agent may be separately added in akneading step, a dispersing step, and a mixing step for adjustingviscosity after the dispersion. In order to manufacture the magnetictape, a well-known manufacturing technology of the related art can beused in various steps. In the kneading step, preferably, a kneaderhaving a strong kneading force such as an open kneader, a continuouskneader, a pressure kneader, or an extruder is used. For details of thekneading processes, descriptions disclosed in JP1989-106338A(JP-H01-106338A) and JP1989-079274A (JP-H01-079274A) can be referred to.As a dispersing device, a well-known dispersing device can be used.Further, the ferromagnetic powder and the abrasive can be separatelydispersed. More specifically, the different dispersion means a method ofpreparing a magnetic layer forming composition through a step of mixingan abrasive liquid including an abrasive and a solvent (here,substantially not including ferromagnetic powder) with a magnetic liquidincluding ferromagnetic powder, a solvent, and a binding agent. Thephrase “substantially not including ferromagnetic powder” means that noferromagnetic powder is added as a constitutive component of theabrasive liquid, and a trace amount of ferromagnetic powder is allowedto exist as an unintentionally mixed impurity. Regarding ΔN, a value ofΔN tends to increase as the dispersion condition of the magnetic liquidis intensified. For example, a value of ΔN tends to increase as thedispersion time of the magnetic liquid increases. It is considered thatthis is because there is a tendency that as the dispersion time of themagnetic liquid is longer, dispersibility of the ferromagnetic powder ina coating layer of the magnetic layer forming composition is higher andthe uniformity of the orientation state of the ferromagnetic particlesconfiguring the ferromagnetic powder is higher by an orientationprocess. In addition, as the dispersion time for mixing and dispersingthe various components of the non-magnetic layer forming compositionincreases, a value of ΔN tends to increase. The dispersion time of themagnetic liquid and the dispersion time of the non-magnetic layerforming composition may be set so that ΔN of 0.25 or more and 0.40 orless can be realized.

Filtering may be performed by a well-known method in any stage ofpreparing each layer forming composition. The filtering can be performedby using a filter, for example. As the filter used in the filtering, afilter having a pore diameter of 0.01 to 3 μm (for example, filter madeof glass fiber or filter made of polypropylene) can be used, forexample.

Coating Step

The magnetic layer can be formed, for example, by directly coating themagnetic layer forming composition onto the non-magnetic support orperforming multilayer coating of the magnetic layer forming compositionwith the non-magnetic layer forming composition in order or at the sametime. The back coating layer can be formed by coating the back coatinglayer forming composition to a side of the non-magnetic support oppositeto a side provided with the magnetic layer (or to be provided with themagnetic layer). Moreover, a coating step for forming each layer canalso be performed by being divided into steps of two or more stages. Forexample, in an aspect, the magnetic layer forming composition can becoated in steps divided into two or more stages. In this case, a dryingprocess may or may not be performed between the coating steps of the twostages. Further, an orientation process may or may not be performedbetween the coating steps of the two stages. For details of the coatingfor forming each layer, a description disclosed in a paragraph 0066 ofJP2010-231843A can be also referred to. Moreover, in the drying stepafter coating each layer forming composition, the well-known technologycan be applied. With regard to the magnetic layer forming composition,as a drying temperature of a coating layer formed by coating themagnetic layer forming composition (hereinafter, also referred to as“coating layer of the magnetic layer forming composition” or simply“coating layer”) is lowered, a value of ΔN tends to increase. The dryingtemperature may be, for example, an atmosphere temperature at which thedrying step is performed, and may be set so that ΔN of 0.25 or more and0.40 or less can be realized.

Other Steps

For details of various other steps for manufacturing the magnetic tape,descriptions disclosed in paragraphs 0067 to 0070 of JP2010-231843A canbe referred to.

For example, preferably, the coating layer of the magnetic layer formingcomposition is subjected to an orientation process while the coatinglayer is in a wet state. From a viewpoint of easiness of realizing ΔN of0.25 or more and 0.40 or less, as the orientation process, a processperformed by disposing a magnet so that a magnetic field is appliedperpendicularly to a surface of the coating layer of the magnetic layerforming composition (that is, a vertical orientation process) ispreferable. An intensity of the magnetic field during an orientationprocess may be set so that ΔN of 0.25 or more and 0.40 or less can berealized. Moreover, in a case of performing the coating step of themagnetic layer forming composition by coating steps of two or morestages, it is preferable to perform an orientation process at leastafter the last coating process, and it is more preferable to perform avertical orientation process at least after the last coating process.For example, in a case where a magnetic layer is formed by coating stepsof two stages, a drying process can be performed without performing anorientation process after a coating process of a first stage, and then acoating layer formed in a coating step of a second stage can besubjected to an orientation process. For the orientation process, thevarious well-known technologies such as descriptions disclosed in aparagraph 0052 of JP2010-024113A can be used. For example, a verticalorientation process can be performed by a well-known method such as amethod using a polar opposing magnet. In an orientation zone, a dryingspeed of the coating layer can be controlled depending on a temperatureand a flow rate of dry air and/or a transportation speed of the magnetictape in the orientation zone. In addition, the coating layer may bepreliminarily dried before the transportation to the orientation zone.

In addition, a calendering process can be performed at any stage afterthe coating layer of the magnetic layer forming composition is dried.For conditions of the calendering process, for example, descriptiondisclosed in a paragraph 0026 of JP2010-231843A can be referred to. As acalender temperature (a surface temperature of a calender roll)increases, a value of ΔN tends to increase. The calender temperature maybe set so that ΔN of 0.25 or more and 0.40 or less can be realized.

Servo Pattern Formation

The magnetic tape has a timing-based servo pattern in the magneticlayer. FIG. 14 shows a disposition example of a region (servo band) inwhich the timing-based servo pattern is formed and a region (data band)which is interposed between two servo bands. FIG. 15 shows a dispositionexample of the timing-based servo pattern. Specific examples of a shapeof the timing-based servo pattern are shown in FIGS. 15 to 17 and FIGS.19 to 21. Here, the disposition example and/or the shape shown in eachdrawing is merely an example, and a servo pattern, a servo band, and adata band may be formed and disposed in a shape and a dispositionaccording to a type of the magnetic tape apparatus (drive). Further, fora shape and a disposition of the timing-based servo pattern, it ispossible to apply the well-known technology such as disposition examplesillustrated in, for example, FIG. 4, FIG. 5, FIG. 6, FIG. 9, FIG. 17,and FIG. 20 of U.S. Pat. No. 5,689,384A without any limitation.

The servo pattern can be formed by magnetizing a specific region of themagnetic layer with the servo write head mounted on a servo writer. Inthe timing-based servo system, for example, a servo signal is obtainedby reading pairs of non-parallel servo patterns (also referred to as“servo stripes”) continuously disposed in plural in a longitudinaldirection of a magnetic tape by a servo element.

In an aspect, as shown in JP2004-318983A, information indicating a servoband number (referred to as “servo band ID (identification)” or “UDIM(Unique Data Band Identification Method) information”) is embedded ineach servo band. This servo band ID is recorded by shifting a specificone of the plurality of pairs of the servo patterns in the servo band sothat positions thereof are relatively displaced in a longitudinaldirection of the magnetic tape. Specifically, a way of shifting thespecific one of the plurality of pairs of servo patterns is changed foreach servo band. Accordingly, the recorded servo band ID is unique foreach servo band, and thus, the servo band can be uniquely specified onlyby reading one servo band with a servo element.

As a method for uniquely specifying a servo band, there is a methodusing a staggered method as shown in ECMA (European ComputerManufacturers Association)-319. In this staggered method, a group ofpairs of non-parallel servo patterns (servo stripes) disposedcontinuously in plural in a longitudinal direction of the magnetic tapeis recorded so as to be shifted in a longitudinal direction of themagnetic tape for each servo band. Since this combination of shiftingmethods between adjacent servo bands is unique throughout the magnetictape, it is possible to uniquely specify a servo band in a case ofreading a servo pattern with two servo elements.

As shown in ECMA-319, information indicating a position of the magnetictape in the longitudinal direction (also referred to as “LPOS(Longitudinal Position) information”) is usually embedded in each servoband. This LPOS information is also recorded by shifting the positionsof the pair of servo patterns in the longitudinal direction of themagnetic tape, as the UDIM information. Here, unlike the UDIMinformation, in this LPOS information, the same signal is recorded ineach servo band.

It is also possible to embed, in the servo band, the other informationdifferent from the above UDIM information and LPOS information. In thiscase, the embedded information may be different for each servo band asthe UDIM information or may be common to all servo bands as the LPOSinformation.

As a method of embedding information in the servo band, it is possibleto employ a method other than the above. For example, a predeterminedcode may be recorded by thinning out a predetermined pair from the groupof pairs of servo patterns.

The servo write head has a pair of gaps corresponding to the pair ofservo patterns as many as the number of servo bands. Usually, a core anda coil are connected to each pair of gaps, and by supplying a currentpulse to the coil, a magnetic field generated in the core can causegeneration of a leakage magnetic field in the pair of gaps. In a case offorming the servo pattern, by inputting a current pulse while runningthe magnetic tape on the servo write head, the magnetic patterncorresponding to the pair of gaps is transferred to the magnetic tape toform the servo pattern. A width of each gap can be appropriately setaccording to a density of the servo pattern to be formed. The width ofeach gap can be set to, for example, 1 μm or less, 1 to 10 μm, 10 μm ormore, and the like.

Before the servo pattern is formed on the magnetic tape, the magnetictape is usually subjected to a demagnetization (erasing) process. Thiserasing process can be performed by applying a uniform magnetic field tothe magnetic tape using a direct current magnet or an alternatingcurrent magnet. The erasing process includes direct current (DC) erasingand alternating current (AC) erasing. AC erasing is performed bygradually decreasing an intensity of the magnetic field while reversinga direction of the magnetic field applied to the magnetic tape. On theother hand, DC erasing is performed by applying a unidirectionalmagnetic field to the magnetic tape. As the DC erasing, there are twomethods. A first method is horizontal DC erasing of applying a magneticfield in one direction along a longitudinal direction of the magnetictape. A second method is vertical DC erasing of applying a magneticfield in one direction along a thickness direction of the magnetic tape.The erasing process may be performed on the entire magnetic tape or maybe performed for each servo band of the magnetic tape.

A direction of the magnetic field of the servo pattern to be formed isdetermined according to a direction of the erasing. For example, in acase where the horizontal DC erasing is performed to the magnetic tape,the servo pattern is formed so that the direction of the magnetic fieldis opposite to the direction of the erasing. Therefore, an output of aservo signal obtained by reading the servo pattern can be increased. Asshown in JP2012-053940A, in a case where a pattern is transferred to,using the gap, a magnetic tape that has been subjected to vertical DCerasing, a servo signal obtained by reading the formed servo pattern hasa monopolar pulse shape. On the other hand, in a case where a pattern istransferred to, using the gap, a magnetic tape that has been subjectedto horizontal DC erasing, a servo signal obtained by reading the formedservo pattern has a bipolar pulse shape.

The magnetic tape described above is usually accommodated in a magnetictape cartridge and the magnetic tape cartridge is mounted in themagnetic tape apparatus.

Magnetic Tape Cartridge

An aspect of the present invention relates to a magnetic tape cartridgecomprising the above magnetic tape.

Details of the magnetic tape included in the magnetic tape cartridge areas described above.

In the magnetic tape cartridge, generally, the magnetic tape isaccommodated inside a cartridge body in a state of being wound around areel. The reel is rotatably provided inside the cartridge body. As themagnetic tape cartridge, a single reel type magnetic tape cartridgehaving one reel inside the cartridge body and a dual reel type magnetictape cartridge having two reels inside the cartridge body are widelyused. In a case where the single reel type magnetic tape cartridge ismounted on a magnetic tape apparatus (drive) for recording and/orreproducing information (magnetic signal) on the magnetic tape, themagnetic tape is pulled out of the magnetic tape cartridge to be woundaround the reel on the drive side. A magnetic head is disposed in amagnetic tape transportation path from the magnetic tape cartridge to awinding reel. Feeding and winding of the magnetic tape are performedbetween a reel (supply reel) on the magnetic tape cartridge side and areel (winding reel) on the drive side. During this time, information isrecorded and/or reproduced as the magnetic head and the magnetic layersurface of the magnetic tape come into contact with each other to beslid on each other. On the other hand, in the dual reel type magnetictape cartridge, both the supply reel and the winding reel are providedinside the magnetic tape cartridge. The magnetic tape cartridge may beeither a single reel type or a dual reel type magnetic tape cartridge.The magnetic tape cartridge has only to include the magnetic tapeaccording to the aspect of the present invention, and the well-knowntechnology can be applied to the others. For the aspect of the magnetictape cartridge, the above-mentioned description regarding the magnetictape cartridge 12 in FIG. 1 can be referred to.

Magnetic Tape Apparatus

An aspect of the present invention relates to a magnetic tape apparatuscomprising: the above described magnetic tape; a reading element unit;and an extraction unit, in which the reading element unit includes aplurality of reading elements each of which reads data from a specifictrack region including a reading target track in a track region includedin the magnetic tape, and the extraction unit performs a waveformequalization process with respect to each reading result for eachreading element, to extract, from the reading result, data derived fromthe reading target track. Such a magnetic tape apparatus is as describedin detail above.

EXAMPLES

Hereinafter, the present invention will be described with reference toexamples. Here, the present invention is not limited to aspects shown inthe examples. Unless otherwise noted, “parts” and “%” described beloware based on mass. In addition, steps and evaluations described beloware performed in an environment of an atmosphere temperature of 23°C.±1° C., unless otherwise noted. “eq” in the following description isan equivalent and is a unit that cannot be converted into SI unit.

An activation volume in Table 1 is a value obtained by the methoddescribed above for each ferromagnetic powder using a vibrating samplemagnetometer (manufactured by Toei Kogyo Co., Ltd.).

Manufacturing of Magnetic Tape

Example 1

Preparation of Abrasive Liquid

3.0 parts of 2,3-dihydroxynaphthalene (manufactured by Tokyo ChemicalIndustry Co., Ltd.), 31.3 parts of a 32% solution (solvent is a mixedsolvent of methyl ethyl ketone and toluene) of a SO₃Na group-containingpolyester polyurethane resin (UR-4800 (SO₃Na group: 0.08 meq/g)manufactured by Toyobo Co., Ltd.), and 570.0 parts of a mixed solutionof methyl ethyl ketone and cyclohexanone (mass ratio of 1:1) as asolvent were mixed with respect to 100.0 parts of alumina powder (HIT-80manufactured by Sumitomo Chemical Co., Ltd) having a gelatinizationratio of approximately 65% and a BET specific surface area of 20 m²/g,and this mixture was dispersed in the presence of zirconia beads by apaint shaker for 5 hours. After the dispersion, the dispersion liquidand the beads were separated by a mesh and an alumina dispersion wasobtained.

Preparation of Magnetic Layer Forming Composition

Magnetic Liquid Plate-shaped hexagonal barium ferrite powder 100.0 partsActivation volume: see Table 1, Average plate 3.5 shape ratio: SO₃Nagroup-containing polyurethane resin see Table 1 Weight-average molecularweight: 70,000, SO₃Na 150.0 parts group: see Table 1 contentCyclohexanone Methyl ethyl ketone 150.0 parts Abrasive Liquid Aluminadispersion prepared above 6.0 parts Silica Sol (Protrusion Forming AgentLiquid) Colloidal silica (Average particle size: 100 nm) 2.0 partsMethyl ethyl ketone 1.4 parts Other Components Stearic acid 2.0 partsButyl stearate 2.0 parts Polyisocyanate (CORONATE (registered trademark)2.5 parts by Tosoh manufactured Corporation) Finishing Additive SolventCyclohexanone 200.0 parts Methyl ethyl ketone 200.0 parts

Preparation Method

The magnetic liquid was prepared by beads-dispersing various componentsof the magnetic liquid using beads as a dispersion medium in a batchtype vertical sand mill. As beads, zirconia beads (bead diameter: seeTable 1) were used, and beads-dispersion was performed for the timeshown in Table 1 (magnetic liquid beads-dispersion time).

The magnetic liquid obtained in this manner, the abrasive liquid, silicasol, other components, and finishing additive solvent were mixed withone another and beads-dispersed for 5 minutes, and then the treatment(ultrasonic dispersion) was performed with a batch type ultrasonicdevice (20 kHz, 300 W) for 0.5 minutes. Thereafter, the resultantdispersion liquid was filtered using a filter having a pore diameter of0.5 μm, and the magnetic layer forming composition was prepared.

Preparation of Non-Magnetic Layer Forming Composition

Among various components of the non-magnetic layer forming compositiondescribed below, components other than stearic acid, butyl stearate,cyclohexanone, and methyl ethyl ketone were beads-dispersed using abatch type vertical sand mill (dispersion medium: zirconia beads (beaddiameter: 0.1 mm), dispersion time: see Table 1), and thus a dispersionliquid was obtained. Thereafter, the remaining components were addedinto the obtained dispersion liquid and were stirred by a dissolverstirrer. Next, the obtained dispersion liquid was filtered using afilter (pore diameter: 0.5 μm), and a non-magnetic layer formingcomposition was prepared.

Non-magnetic inorganic powder: α-iron oxide 100.0 parts Average particlesize (Average long axis length): 0.15 μm Average acicular ratio: 7 BETspecific surface area: 52 m²/g Carbon black 20.0 parts Average particlesize: 20 nm Electron beam-curable vinyl chloride copolymer 13.0 partsElectron beam-curable polyurethane resin 6.0 parts Stearic acid 1.0 partButyl stearate 1.0 part Cyclohexanone 300.0 parts Methyl ethyl ketone300.0 parts

Preparation of Back Coating Layer Forming Composition

Among various components of the back coating layer forming compositiondescribed below, components other than stearic acid, butyl stearate,polyisocyanate and cyclohexanone were kneaded and diluted by an openkneader, and thus a mixed liquid was obtained. Thereafter, the obtainedmixed liquid was subjected to dispersion processes of 12 passes by ahorizontal beads mill using zirconia beads having a bead diameter of 1.0mm, with setting a retention time per pass to 2 minutes at a beadfilling rate of 80 vol % and a rotor tip circumferential speed of 10m/sec. Thereafter, the remaining components were added into the obtaineddispersion liquid and were stirred by a dissolver stirrer. Next, theobtained dispersion liquid was filtered using a filter (pore diameter:1.0 μm), and thus a back coating layer forming composition was prepared.

Non-magnetic inorganic powder: α-iron oxide 80.0 parts Average particlesize (Average long axis length): 0.15 μm Average acicular ratio: 7 BETspecific surface area: 52 m²/g Carbon black 20.0 parts Average particlesize: 20 nm Vinyl chloride copolymer 13.0 parts Sulfonategroup-containing polyurethane resin 6.0 parts Phenylphosphonic acid 3.0parts Methyl ethyl ketone 155.0 parts Stearic acid 3.0 parts Butylstearate 3.0 parts Polyisocyanate 5.0 parts Cyclohexanone 355.0 parts

Manufacturing of Magnetic Tape

The non-magnetic layer forming composition was coated onto a biaxiallystretched polyethylene naphthalate support and was dried, and then, anelectron beam was emitted with an energy of 40 kGy at an accelerationvoltage of 125 kV, and thus a non-magnetic layer was formed.

The magnetic layer forming composition was coated onto a surface of theformed non-magnetic layer so that a thickness after the drying becomes50 nm, and thus a coating layer was formed. While this coating layer isin a wet state, a magnetic field of an intensity described in a“Formation and orientation of magnetic layer” field in Table 1 wasapplied onto a surface of the coating layer in a direction perpendicularthereto using a polar opposing magnet in an atmosphere at an atmospheretemperature (magnetic layer drying temperature) described in Table 1,and a vertical orientation process and a drying process were performed,and thus a magnetic layer was formed.

After that, the back coating layer forming composition was coated ontothe surface of the support on a side opposite to the surface where thenon-magnetic layer and the magnetic layer are formed, and was dried.

After that, a surface smoothing process (calendering process) wasperformed using a calender roll configured with only a metal roll, underconditions of a calendering process speed of 80 m/min, a linear pressureof 300 kg/cm (294 kN/m), and a calender temperature (surface temperatureof a calender roll) described in Table 1.

Then, a thermal process was performed in an environment of an atmospheretemperature of 70° C. for 36 hours. After the thermal process, slittingwas performed so as to have a width of ½ inches (1 inch is 0.0254meters), and the surface of the magnetic layer was cleaned by a tapecleaning device in which a nonwoven fabric and a razor blade areattached to a device including a sending and winding device of a slitproduct so as to press the surface of the magnetic layer. After that, ina state where the magnetic layer of the obtained magnetic tape wasdemagnetized, a servo pattern (timing-based servo pattern) having adisposition and a shape according to an LTO Ultrium format was formed onthe magnetic layer by a servo write head (leakage magnetic field: 247kA/m) mounted on the servo writer. Accordingly, a magnetic tape ofExample 1 including data bands, servo bands, and guide bands in thedisposition according to the LTO Ultrium format in the magnetic layer,and including servo patterns having the disposition and the shapeaccording to the LTO Ultrium format on the servo band was obtained.

Example 3 and Comparative Examples 1, 3, and 5

A magnetic tape was manufactured in the same manner as in Example 1except that various items shown in Table 1 were changed as shown inTable 1.

In Table 1, in comparative examples described as “No orientationprocess” in the “Formation and orientation of magnetic layer” field, amagnetic tape was manufactured without performing an orientation processon the coating layer of the magnetic layer forming composition.

Comparative Example 2

A magnetic tape was manufactured in the same manner as in Example 1except that hexagonal barium ferrite powder having an activation volumeshown in Table 1 was used as ferromagnetic powder, various conditionswere changed as shown in Table 1, and a servo write head having aleakage magnetic field of 366 kA/m was used as the servo write head.

Example 2

After forming a non-magnetic layer on a biaxially stretched polyethylenenaphthalate support in the same manner as in Example 1, a magnetic layerforming composition was coated onto a surface of the non-magnetic layerso that a thickness after the drying becomes 25 nm, and thus a firstcoating layer was formed. This first coating layer was passed through anatmosphere having an atmosphere temperature (magnetic layer dryingtemperature) described in Table 1 without applying a magnetic field, andthus a first magnetic layer (without orientation process) was formed.

Thereafter, the magnetic layer forming composition was coated onto asurface of the first magnetic layer so that a thickness after the dryingbecomes 25 nm, and thus a second coating layer was formed. While thissecond coating layer is in a wet state, a magnetic field of an intensitydescribed in a “Formation and orientation of magnetic layer” field inTable 1 was applied onto a surface of the second coating layer in adirection perpendicular thereto using a polar opposing magnet in anatmosphere at an atmosphere temperature (magnetic layer dryingtemperature) shown in Table 1, and a vertical orientation process and adrying process were performed, and thus a second magnetic layer wasformed.

A magnetic tape was manufactured in the same manner as in Example 1except that the multilayer magnetic layer was formed as described above.

Comparative Example 4

After forming a non-magnetic layer on a biaxially stretched polyethylenenaphthalate support in the same manner as in Example 1, a magnetic layerforming composition was coated onto a surface of the non-magnetic layerso that a thickness after the drying becomes 25 nm, and thus a firstcoating layer was formed. While this first coating layer is in a wetstate, a magnetic field of an intensity described in a “Formation andorientation of magnetic layer” field in Table 1 was applied onto asurface of the first coating layer in a direction perpendicular theretousing a polar opposing magnet in an atmosphere at an atmospheretemperature (magnetic layer drying temperature) described in Table 1,and a vertical orientation process and a drying process were performed,and thus a first magnetic layer was formed.

Thereafter, the magnetic layer forming composition was coated onto asurface of the first magnetic layer so that a thickness after the dryingbecomes 25 nm, and thus a second coating layer was formed. This secondcoating layer was passed through an atmosphere having an atmospheretemperature (magnetic layer drying temperature) described in Table 1without applying a magnetic field, and thus a second magnetic layer(without orientation process) was formed.

A magnetic tape was manufactured in the same manner as in Example 1except that the multilayer magnetic layer was formed as described above.

Evaluation of Physical Properties

(1) Thicknesses of Non-Magnetic Support and Each Layer

The thicknesses of the magnetic layer, the non-magnetic layer, thenon-magnetic support, and the back coating layer of each manufacturedmagnetic tape were measured by the following method. As a result of themeasurement, in any magnetic tape, the thickness of the magnetic layerwas 50 nm, the thickness of the non-magnetic layer was 0.7 μm, thethickness of the non-magnetic support was 5.0 μm, and the thickness ofthe back coating layer was 0.5 μm.

The thicknesses of the magnetic layer, the non-magnetic layer, and thenon-magnetic support measured here were used for the followingrefractive index calculation.

(i) Manufacturing of Cross Section Observing Sample

According to a method described in paragraphs 0193 and 0194 ofJP2016-177851A, a cross section observing sample including the entireregion in the thickness direction from the magnetic layer side surfaceof the magnetic tape to the back coating layer side surface wasmanufactured.

(ii) Thickness Measurement

The manufactured sample was observed with a STEM, and a STEM image wascaptured. This STEM image is a STEM-HAADF (high-angle annular darkfield) image captured at an acceleration voltage of 300 kV and animaging magnification of 450,000 times, and imaging was performed sothat the entire region in the thickness direction from the magneticlayer side surface of the magnetic tape to the back coating layer sidesurface was included in one image. In such an obtained STEM image, astraight line connecting both ends of a line segment representing themagnetic layer surface was determined as a reference line representingthe magnetic layer side surface of the magnetic tape. The straight lineconnecting both ends of the above-mentioned line segment is, forexample, a straight line connecting an intersection between a left sideof the image of the STEM image (a shape thereof is rectangular orsquare) and the line segment, and an intersection between a right sideof the STEM image and the line segment, in a case where the STEM imageis captured so that the magnetic layer side of the cross sectionobserving sample is positioned at an upper portion of the image and theback coating layer side is positioned at a lower portion of the image.Similarly, a reference line representing an interface between themagnetic layer and the non-magnetic layer, a reference line representingan interface between the non-magnetic layer and the non-magneticsupport, a reference line representing an interface between thenon-magnetic support and the back coating layer, and a reference linerepresenting the back coating layer side surface of the magnetic tapewere determined.

The thickness of the magnetic layer was obtained as the shortestdistance from one randomly selected portion on the reference linerepresenting the magnetic layer side surface of the magnetic tape to thereference line representing an interface between the magnetic layer andthe non-magnetic layer. Similarly, the thicknesses of the non-magneticlayer, the non-magnetic support, and the back coating layer wereobtained.

(2) ΔN of Magnetic Layer

In the following, M-2000U manufactured by Woollam Co. was used as anellipsometer. Creation and fitting of the two-layer model or theone-layer model were performed using WVASE32 manufactured by Woollam Co.as analysis software.

(i) Refractive Index Measurement of Non-Magnetic Support

A measurement sample was cut out from each magnetic tape. An unusedcloth was soaked with fresh methyl ethyl ketone, the back coating layerof the measurement sample was removed by being wiped off using thiscloth to expose the non-magnetic support surface, and then this surfacewas roughened with sand paper so that a reflection ray on the exposedsurface is not detected in the measurement with an ellipsometer to beperformed thereafter.

Thereafter, an unused cloth was soaked with fresh methyl ethyl ketone,the magnetic layer and the non-magnetic layer of the measurement samplewere removed by being wiped off using this cloth, and then a siliconwafer surface and the roughened surface were attached to each otherusing static electricity, and thus, the measurement sample was disposedon a silicon wafer so that the non-magnetic support surface exposed byremoving the magnetic layer and the non-magnetic layer (hereinafter,referred to as a “magnetic layer side surface of the non-magneticsupport”) is directed upward.

Using an ellipsometer, an incidence ray was made incident on themagnetic layer side surface of the non-magnetic support of themeasurement sample on the silicon wafer as described above, and Δ and Ψwere measured. Refractive indexes of the non-magnetic support (arefractive index in a longitudinal direction, a refractive index in awidth direction, a refractive index in a thickness direction, measuredby making an incidence ray incident in a longitudinal direction, and arefractive index in a thickness direction, measured by making anincidence ray incident in a width direction) were obtained by the methoddescribed above using the obtained measurement value and the thicknessof the non-magnetic support obtained in (2) above.

(ii) Refractive Index Measurement of Non-Magnetic Layer

A measurement sample was cut out from each magnetic tape. An unusedcloth was soaked with fresh methyl ethyl ketone, the back coating layerof the measurement sample was removed by being wiped off using thiscloth to expose the non-magnetic support surface, and then this surfacewas roughened with sand paper so that a reflection ray on the exposedsurface is not detected in the measurement with a spectroscopicellipsometer to be performed thereafter.

After that, an unused cloth was soaked with fresh methyl ethyl ketone,the magnetic layer was removed by wiping off lightly the magnetic layersurface of the measurement sample using this cloth to expose thenon-magnetic layer surface, and then the measurement sample was disposedon a silicon wafer in the same manner as (i) above.

For the non-magnetic layer surface of the measurement sample on thissilicon wafer, measurement was performed using an ellipsometer, andrefractive indexes of the non-magnetic layer (a refractive index in alongitudinal direction, a refractive index in a width direction, arefractive index in a thickness direction, measured by making anincidence ray incident in a longitudinal direction, and a refractiveindex in a thickness direction, measured by making an incidence rayincident in a width direction) were obtained by the method describedabove in a spectral ellipsometry.

(iii) Refractive Index Measurement of Magnetic Layer

A measurement sample was cut out from each magnetic tape. An unusedcloth was soaked with fresh methyl ethyl ketone, the back coating layerof the measurement sample was removed by being wiped off using thiscloth to expose the non-magnetic support surface, and then this surfacewas roughened with sand paper so that a reflection ray on the exposedsurface is not detected in the measurement with a spectroscopicellipsometer to be performed thereafter.

After that, the measurement sample was disposed on the silicon wafer inthe same manner as in the above (i).

For the magnetic layer surface of the measurement sample on this siliconwafer, measurement was performed using an ellipsometer, and refractiveindexes of the magnetic layer (a refractive index Nx in a longitudinaldirection, a refractive index Ny in a width direction, a refractiveindex Nz₁ in a thickness direction, measured by making an incidence rayincident in a longitudinal direction, and a refractive index Nz₂ in athickness direction, measured by making an incidence ray incident in awidth direction) were obtained by the method described above in aspectral ellipsometry. From the obtained values, Nxy and Nz wereobtained and further, an absolute value ΔN of a difference therebetweenwas obtained. For any of the magnetic tapes of the examples and thecomparative examples, the obtained Nxy was a value larger than Nz (thatis, Nxy>Nz).

(3) Vertical Direction Squareness Ratio (SQ)

A vertical direction squareness ratio of the magnetic tape is asquareness ratio measured in a vertical direction of the magnetic tape.The “vertical direction” described with respect to the squareness ratiorefers to a direction orthogonal to the magnetic layer surface. For eachmagnetic tape of the examples and the comparative examples, using avibration sample type magnetometer (manufactured by Toei Kogyo Co.,Ltd.), at a measurement temperature of 23° C.±1° C., an externalmagnetic field was applied to the magnetic tape at a maximum externalmagnetic field of 1194 kA/m (15 kOe) and a scanning speed of 4.8kA/m/sec (60 Oe/sec), and the vertical direction squareness ratio wasobtained. The measurement value is a value after diamagnetic fieldcorrection, and is obtained as a value obtained by subtractingmagnetization of a sample probe of the vibration sample typemagnetometer as background noise from the squareness ratio. In anaspect, the vertical direction squareness ratio of the magnetic tape ispreferably 0.60 or more and 1.00 or less. Moreover, in an aspect, thevertical direction squareness ratio of the magnetic tape may be, forexample, 0.90 or less, 0.85 or less, or 0.80 or less, and may exceedthese values.

(4) Difference (L_(99.9)−L_(0.1))

A difference (L_(99.9)−L_(0.1)) was obtained for each magnetic tape ofthe examples and the comparative examples by the following method.

Using Dimension 3100 manufactured by Bruker as a magnetic forcemicroscope in a frequency modulation mode and SSS-MFMR (nominalcurvature radius of 15 nm) manufactured by Nanoworld AG as a probe, in arange of 90 μm×90 μm of the magnetic layer surface of the magnetic tapeon which the servo pattern was formed, rough measurement was performedat a pitch of 100 nm to extract a servo pattern (magnetization region).A distance between a magnetic layer surface and a probe distal endduring magnetic force microscopy was 20 nm. Since the above measurementrange includes the five servo patterns of the A burst formed inaccordance with the LTO Ultrium format, these five servo patterns wereextracted.

The magnetic profile was obtained by measuring the vicinity of theboundary between the magnetization region and the non-magnetizationregion at a pitch of 5 nm, using the magnetic force microscope and theprobe, in a downstream edge of each servo pattern in a runningdirection. Since the obtained magnetic profile was inclined at an angleα=12°, rotation correction was performed by analysis software so thatthe angle α=0°.

The measurement was performed at three different portions on themagnetic layer surface. Each measurement range includes five servopatterns of the A burst.

Thereafter, the difference (L_(99.9)−L_(0.1)) was obtained by the methoddescribed above using analysis software. As analysis software, MATLABmanufactured by MathWorks was used. Such an obtained difference(L_(99.9)−L_(0.1)) is shown in Table 1.

Performance Evaluation

(1) The recording of data was performed on the magnetic layer of eachmagnetic tape of the examples and the comparative examples by using arecording and reproducing head mounted on TS1155 tape drive manufacturedby IBM Corporation, under recording conditions of a rate of 6 m/s, alinear recording density of 600 kbpi (255 bit PRBS), and a track pitchof 2 μm. The unit kbpi is a unit of linear recording density (cannot beconverted into SI unit system). The PRBS is an abbreviation of PseudoRandom Bit Sequence.

By the recording, a specific track region, where the reading targettrack is positioned, is formed on the magnetic layer of each magnetictape between two adjacent tracks, that is, between a first noise mixingsource track and a second noise mixing source track.

(2) The following data reading was performed as a model experiment ofperforming the data reading using the reading element unit including tworeading elements disposed in an adjacent state. In the following modelexperiment, the data reading was performed by bringing the magneticlayer surface and the reading element into contact with each other to beslid on each other.

The reading was started in a state where the magnetic head including asingle reading element was disposed so that the center of the readingtarget track in the tape width direction coincides with the center ofthe reading element in the track width direction, and a first datareading was performed. During this first data reading, the servo patternwas read by the servo element, and the tracking in the timing-basedservo system was also performed. In addition, the data reading operationwas performed by the reading element synchronously with the servopattern reading operation.

Then, the position of the same magnetic head was deviated in the tapewidth direction (one adjacent track side) by 500 nm, and a second datareading was performed, in the same manner as in the first data reading.The two times of data reading described above were respectivelyperformed under reading conditions of a reproducing element width of 0.2μm, a rate of 4 m/s, and a sampling rate:bit rate of 1.25 times.

A reading signal obtained by the first data reading was input to anequalizer, and the waveform equalization process according to thedeviation amount of the positions between the magnetic tape and themagnetic head (reading element) of the first data reading was performed.This waveform equalization process is a process performed as follows. Aratio between an overlapping region of the reading element and thereading target track and an overlapping region of the reading elementand the adjacent track is specified from the deviation amount of theposition obtained by reading the servo pattern formed at regular cycleby the servo element. A convolution arithmetic operation of a tapcoefficient derived from this specific ratio using an arithmeticexpression, was performed with respect to the reading signal, andaccordingly, the waveform equalization process was performed. Thearithmetic expression is an arithmetic expression in which ExtendedPartial Response class 4 (EPR4) is set as a reference waveform (target).Regarding a reading signal obtained in the second data reading, thewaveform equalization process was performed in the same manner.

By performing a phase matching process (two-dimensional signal process)of the two reading signals subjected to the waveform equalizationprocess, a reading signal which was expected to be obtained by thereading element unit including two reading elements disposed in anadjacent state (reading element pitch=500 nm) was obtained. Regardingthe reading signal obtained by doing so, an SNR at a signal detectionpoint was calculated.

(3) The operation of (2) was repeated while performing track off-set ofthe position of the reading element at the start of the first datareading to the first noise mixing source track and the second noisemixing source track, respectively from the center of the reading targettrack in the tape width direction at interval of 0.1 μm, and an envelopeof the SNR with respect to the track position was obtained.

In each of the examples and the comparative examples, the envelope ofthe SNR was obtained reading only the first data reading result (thatis, data reading result obtained with only a single element).

(4) The envelope of the SNR obtained regarding the data reading resultobtained with only the single element was set as a reference envelope,and the SNR decreased from the SNR of the track center of the referenceenvelope by −3 dB was set as an SNR lower limit value. Regarding eachenvelope, the maximum track off-set amount equal to or greater than thelower limit value was set as an allowable track off-set amount. Inrespective examples and the comparative examples, a rate of increase ofthe allowable track off-set amount with respect to the allowable trackoff-set amount obtained with only the single element was obtained as a“rate of increase of the allowable track off-set amount”.

The results described above are shown in Table 1 (Tables 1-1 to 1-3).

TABLE 1-1 Example 1 Example 2 Example 3 Ferromagnetic Activation 1600nm³ 1600 nm³ 1600 nm³ powder volume Magnetic liquid beads dispersiontime 50 hours 50 hours 50 hours Magnetic liquid dispersion bead diameter0.1 mm 0.1 mm 0.1 mm Magnetic Liquid: SO₃Na group content 330 eq/ton 330eq/ton 330 eq/ton of polyurethane resin Magnetic Liquid: SO₃Nagroup-containing 15.0 parts 15.0 parts 15.0 parts polyurethane resincontent Dispersion time of non-magnetic layer 24 hours 24 hours 24 hoursforming composition Magnetic layer drying temperature 50° C. 50° C. 50°C. Calender temperature 100° C. 100° C. 100° C. Formation andorientation of Vertical Second layer: Vertical magnetic layerorientation vertical orientation 0.5 T orientation 0.5 0.2 T T/Firstlayer: no orientation process Vertical direction squareness ratio 0.660.60 0.60 (SQ) Nxy 1.90 1.95 1.90 Nz 1.60 1.60 1.65 ΔN 0.30 0.35 0.25Difference (L_(99.9) − L_(0.1)) (nm) 150 150 150 Rate of increase ofallowable track 30 35 25 off-set amount (%)

TABLE 1-2 Comparative Compar-tive Comparative Example 1 Example 2Example 3 Ferromagnetic Activation 1600 nm³ 2500 nm³ 1600 nm³ powdervolume Magnetic liquid beads dispersion time 6 hours 6 hours 50 hoursMagnetic liquid dispersion bead diameter 1 mm 1 mm 0.1 mm MagneticLiquid: SO₃Na group content 60 eq/ton 60 eq/ton 330 eq/ton ofpolymethane resin Magnetic Liquid: SO₃Na group-containing 25.0 parts25.0 parts 15.0 parts polyurethane resin content Dispersion time ofnon-magnetic layer 3 hours 3 hours 24 hours forming composition Magneticlayer drying temperature 70° C. 70° C. 50° C. Calender temperature 100°C. 100° C. 100° C. Formation and orientation of No orientation Noorientation No orientation magnetic layer process process processVertical direction squareness ratio 0.50 0.50 0.53 (SQ) Nxy 1.90 1.901.90 Nz 1.80 1.80 1.70 ΔN 0.10 0.10 0.20 Difference (L_(99.9) − L_(0.1))(nm) 260 155 230 Rate of increase of allowable track 2 15 5 off-setamount (%)

TABLE 1-3 Comparative Comparative Example 4 Example 5 Ferro- Activation1600 nm³ 1600 nm³ magnetic volume powder Magnetic liquid beadsdispersion 50 hours 96 hours time Magnetic liquid dispersion bead 0.1 mm0.1 mm diameter Magnetic Liquid: SO₃Na 330 eq/ton 330 eq/ton groupcontent of polyurethane resin Magnetic Liquid: SO₃Na group- 15.0 parts10.0 parts containing polyurethane resin content Dispersion time ofnon-magnetic 24 hours 48 hours layer forming composition Magnetic layerdrying temperature 50° C. 30° C. Calender temperature 100° C. 110° C.Formation and orientation of Second layer: vertical magnetic layer noorientation orientation process/ 0.5 T First layer: vertical orientation0.5 T Vertical direction 0.60 0.80 squareness ratio (SQ) Nxy 1.90 2.20Nz 1.70 1.75 ΔN 0.20 0.45 Difference (L_(99.9) − L_(0.1)) 235 250 (nm)Rate of increase of 3 2 allowable track off-set amount (%)

As shown in Table 1, according to the examples, the rate of increase ofthe allowable track off-set amount equal to or greater than 20% could berealized.

A large allowable track off-set amount obtained by the method describedabove is advantageous, from a viewpoint of performing the reproducingwith excellent reproducing quality, even with a small track margin. Fromthis viewpoint, a rate of increase of the allowable track off-set amountis preferably equal to or greater than 20%.

Generally, a squareness ratio is known as an index of a state ofexistence of ferromagnetic powder in the magnetic layer. Here, as shownin Table 1, even in a case of magnetic tapes having the same verticaldirection squareness ratio, values of ΔN in the magnetic tapes aredifferent from one another (for example, Example 2, Example 3, andComparative Example 4). This is considered to indicate that ΔN is avalue that is influenced by other factors in addition to an existingstate of ferromagnetic powder in the magnetic layer.

An aspect of the present invention is useful in magnetic recording whereit is desired to reproduce high density recorded data with excellentreproducing quality.

What is claimed is:
 1. A magnetic tape comprising: a non-magneticsupport; and a magnetic layer including ferromagnetic powder and abinding agent, wherein the magnetic layer has a timing-based servopattern, wherein an edge shape of the timing-based servo pattern,specified by magnetic force microscopy is a shape in which a differenceL_(99.9)−L_(0.1) between a value L_(99.9) of a cumulative distributionfunction of 99.9% and a value L_(0.1) of a cumulative distributionfunction of 0.1% in a position deviation width from an ideal shape ofthe magnetic tape in a longitudinal direction is 180 nm or less, andwherein the absolute value ΔN of the difference between the refractiveindex Nxy of the magnetic layer, measured in an in-plane direction andthe refractive index Nz of the magnetic layer, measured in a thicknessdirection is 0.25 or more and 0.40 or less.
 2. The magnetic tapeaccording to claim 1, wherein Nxy>Nz and the difference Nxy−Nz betweenthe refractive index Nxy and the refractive index Nz is 0.25 or more and0.40 or less.
 3. The magnetic tape according to claim 1, wherein thetiming-based servo pattern is a linear servo pattern which continuouslyextends from one side of the magnetic tape in a width direction to theother side thereof and is inclined at an angle α with respect to thewidth direction, and wherein the ideal shape is a linear shape extendingin a direction of the angle α.
 4. The magnetic tape according to claim1, wherein the difference L_(99.9)−L_(0.1) is 100 nm or more and 180 nmor less.
 5. The magnetic tape according to claim 1, further comprising:a non-magnetic layer including non-magnetic powder and a binding agentbetween the non-magnetic support and the magnetic layer.
 6. The magnetictape according to claim 1, further comprising: a back coating layerincluding non-magnetic powder and a binding agent on a surface side ofthe non-magnetic support opposite to a surface side provided with themagnetic layer.
 7. A magnetic tape cartridge comprising the magnetictape according to claim
 1. 8. The magnetic tape cartridge according toclaim 7, wherein Nxy>Nz and the difference Nxy−Nz between the refractiveindex Nxy and the refractive index Nz is 0.25 or more and 0.40 or less.9. The magnetic tape cartridge according to claim 7, wherein thetiming-based servo pattern is a linear servo pattern which continuouslyextends from one side of the magnetic tape in a width direction to theother side thereof and is inclined at an angle α with respect to thewidth direction, and wherein the ideal shape is a linear shape extendingin a direction of the angle α.
 10. The magnetic tape cartridge accordingto claim 7, wherein the difference L_(99.9)−L_(0.1) is 100 nm or moreand 180 nm or less.
 11. The magnetic tape cartridge according to claim7, wherein the magnetic tape further comprises a non-magnetic layerincluding non-magnetic powder and a binding agent between thenon-magnetic support and the magnetic layer.
 12. The magnetic tapecartridge according to claim 7, wherein the magnetic tape furthercomprises a back coating layer including non-magnetic powder and abinding agent on a surface side of the non-magnetic support opposite toa surface side provided with the magnetic layer.
 13. A magnetic tapeapparatus comprising: a magnetic tape; a reading element unit; and anextraction unit, wherein the magnetic tape is the magnetic tapeaccording to claim 1, wherein the reading element unit includes aplurality of reading elements each of which reads data from a specifictrack region including a reading target track in a track region includedin the magnetic tape, and wherein the extraction unit performs awaveform equalization process with respect to each reading result foreach reading element, to extract, from the reading result, data derivedfrom the reading target track.
 14. The magnetic tape apparatus accordingto claim 13, wherein Nxy>Nz and the difference Nxy−Nz between therefractive index Nxy and the refractive index Nz is 0.25 or more and0.40 or less.
 15. The magnetic tape apparatus according to claim 13,wherein the timing-based servo pattern is a linear servo pattern whichcontinuously extends from one side of the magnetic tape in a widthdirection to the other side thereof and is inclined at an angle α withrespect to the width direction, and wherein the ideal shape is a linearshape extending in a direction of the angle α.
 16. The magnetic tapeapparatus according to claim 13, wherein the difference L_(99.9)−L_(0.1)is 100 nm or more and 180 nm or less.
 17. The magnetic tape apparatusaccording to claim 13, wherein the magnetic tape further comprises anon-magnetic layer including non-magnetic powder and a binding agentbetween the non-magnetic support and the magnetic layer.
 18. Themagnetic tape apparatus according to claim 13, wherein the magnetic tapefurther comprises a back coating layer including non-magnetic powder anda binding agent on a surface side of the non-magnetic support oppositeto a surface side provided with the magnetic layer.